It is no coincidence that the Zodiac Killer only wrote "in this cipher is my idenity" in the letter he mailed to the San Francisco Chronicle on July 31st 1969, because this one-third of the cipher contained the 18 unsolved characters at its foot. This was also the only letter of the three to begin with "This is the murderer". The other two communications to the San Francisco Examiner and Vallejo Times-Herald began with "I am the killer". This shift in introduction may be completely accidental, may be subconscious or may be completely deliberate on account of the "identity" he is to place at the foot of the cipher. The author of these three communications had deliberately separated them into three parts, and therefore when he was preparing the San Francisco Chronicle letter, one would like to think he was considering the opening line when placing his identity at the end of the cipher. If he was ever going to disclose his identity (but not his name), then logically it would be an extension of "I am the killer" to "I am the Zodiac Killer", and therefore satisfy the quota of 18 unsolved characters required by the cipher. I have inserted "I am the Zodiac Killer" at the end of the opening lines of the San Francisco Chronicle and San Francisco Examiner to show how the revelation of his identity in the Chronicle better suits the introduction of "This is the murderer". 
San Francisco Chronicle: "Dear Editor, This is the murderer of the 2 teenagers last Christmass at Lake Herman + the girl on the 4th of July near the golf course in Vallejo. I am the Zodiac Killer" 
San Francisco Examiner: Dear Editor, I am the killer of the 2 teen-agers last Christmass at Lake Herman and the Girl last 4th of July. I am the Zodiac Killer"     

The Zodiac Killer may have accidentally dropped the word "people" from the San Francisco Chronicle cipher (shown in red above) when he transitioned from one cipher to another, unwittingly missing out this word from his original draft to final version, and thereby forcing him to switch from the intended 12 characters he meant to leave, to a revised 18 characters.To rectify his mistake he simply changed "I am the Zodiac" to "I am the Zodiac Killer". The confirmed murderer of five never used the term "Zodiac Killer" in any of his subsequent communications, opting for "This is the Zodiac speaking", but may have had his hand forced on this occasion. It would have been relatively easy to just rewrite the San Francisco Chronicle cipher, but this was an easy solution. One can see how the Zodiac Killer chose his words in the October 13th 1969 letter, opening up with "This is the Zodiac speaking. I am the murderer of the taxi driver over by Washington St + Maple St last night". He uses the words "I am" because he has already introduced himself as the Zodiac. In the July 31st 1969 San Francisco Chronicle letter he uses the words "This is the murderer" because he has thus far failed to introduce himself, which he reserves for the final line of the cipher, stating "I am the Zodiac (Killer)". It is effectively a reversal of the Paul Stine letter. 
Paul Stine letter: "This is the Zodiac speaking. I am the murderer of the taxi driver".  
San Francisco Chronicle: "This is the murderer of the 2 teenagers. I am the Zodiac Killer"    

The murderer would very quickly introduce himself in the August 4th 1969 'Debut of Zodiac' letter: "This is the Zodiac speaking. In answer to your asking for more details about the good times I have had in Vallejo, I shall be very happy to supply even more material. By the way, are the police having a good time with the code? If not, tell them to cheer up; when they do crack it, they will have me". He was introducing himself as "Zodiac", so when the police did eventually crack the code, in effect, they would have "had Zodiac". 

An anonymous caller in San Francisco declared that whoever devised the code "would have to have a vast knowledge in three fields - surveying, nautical science and marksmanship". How the caller could derive that the triple murderer had a vast knowledge of marksmanship from these attacks is hard to justify, not to mention nautical science and surveying. Was the Zodiac Killer ringing the police and blowing his own trumpet? The murderer did ultimately commit his murders with varied weaponry and did eventually introduce a map and radians into his communications.   

If we are looking for an identity or pseudonym in the 18 unsolved characters of the 408 cipher, then it must include appropriate word usage in order to increase the originally intended 12 characters up to 18 characters. So if the original message was "I am the Zodiac" or "Zodiac Killer", then the author had to supplement it with an extra 6 characters to replace the word "people". The simplest avenue available was to add "Killer" or "I am the", in order to generate these 6 characters. These were all used consecutively in two of the three communications mailed on July 31st 1969, when the Zodiac Killer wrote "I am the killer of the 2 teenagers last Christmass at Lake Herman + the girl last 4th of July" to the San Francisco Examiner and Vallejo Times-Herald.  

The Zodiac Killer had seemingly failed to fully convince Vallejo Police Chief Jack E Stiltz, who was less than satisfied that the letter writer and killer were one and the same, urging the author of the July 31st 1969 letters to send in more details of the crimes. The Zodiac Killer immediately dispatched the 'Debut of Zodiac' letter on August 4th 1969 with the introduction of "This is the Zodiac speaking". Although the Zodiac Killer could add more details of the crimes in this new letter to prove he was the killer, It is conceivable he revealed his pseudonym after only four days to inextricably link himself to the first three letters. The only way he could achieve this beyond any doubt, was to reveal a significant word in the unsolved cipher. Then the police would know for certain when the code was broken, that the author of the August 4th 1969 letter was not only the killer, but the designer of the cryptogram. So he introduced his pseudonym "Zodiac" earlier than he had originally intended and immediately rushed it off to the San Francisco Examiner newspaper on August 4th 1969, before the cryptogram was solved.

​Remember, if Vallejo Police Chief Jack E. Stiltz had not urged the author of the July 31st 1969 letters to send in more details to prove the letter writer was the killer, the 'Debut of Zodiac' letter would likely never have been written and sent to the Examiner. The "Zodiac" would still have been the "killer" by the time of the Paul Stine murder. He revealed his pseudonym to link himself to the San Francisco Chronicle's 18 characters, but unfortunately for him, he clearly underestimated the difficulty of the encryption. The release of his identity or pseudonym "Zodiac" so quickly, may lend credence to its presence in the remainder of the 408 cipher, and by extension, the 18 unsolved characters harboring a genuine and coherent message. 

​"This is the Zodiac speaking. By the way, are the police having a good time with the code? If not, tell them to cheer up; when they do crack it, they will have me".

THE 18 UNSOLVED CHARACTERS [PT1]
THE 18 UNSOLVED CHARACTERS [PT2]
​THE 18 UNSOLVED CHARACTERS [PT3]

The 'Debut of Zodiac' letter was received by the San Francisco Examiner newspaper on August 4th 1969 and immediately turned it over to the Vallejo Police Department for comparison to previous Zodiac correspondence. The FBI files constantly referred to the July 31st 1969 trinity of letters and envelopes, but there was a notable absence of the word "envelope" when referring to the August 4th 1969 communication, and more importantly, on the day it was received.
The FBI files explicitly state that the correspondence was "undated", and sent "anonymously". In the absence of any dated or postmarked envelope, this strongly indicates that the three-page letter was hand delivered by the killer to the offices of the San Francisco Examiner at Third and Market Streets.

The Zodiac Killer painstakingly detailed his first two crimes in the July 31st letters "stating some facts which only I + the police know.", so must have been aghast at the statement of Vallejo Police Chief Jack E Stiltz in the Sunday August 3rd 1969 San Francisco Examiner & Chronicle, wanting more facts to prove the letter writer was the killer. This may explain his eagerness in rushing off his three-page letter to the San Francisco Examiner. He may have considered posting it in a public mailbox, but his apparent desire to back up his claims in the July 31st letters and have it published in the Examiner by Monday afternoon, forced him to opt for the direct route of hand-delivery. 

For 35 years starting in 1965, the San Francisco Chronicle and Examiner operated under a Joint Operating Agreement whereby the Chronicle published a morning paper and the Examiner published in the afternoon. The Examiner published the Sunday paper's news sections and glossy magazine, and the Chronicle contributed the features. Circulation was approximately 100,000 on weekdays and 500,000 on Sundays. Wikipedia.

Below, the Vallejo News Chronicle details the Zodiac Killer's fourth letter to the San Francisco Examiner on Monday August 4th 1969,        

The noticeable absence of the word "envelope" is not the only reason for believing the 'Debut of Zodiac' letter was hand-delivered, when we look at the layout of the 3rd page, where the Zodiac Killer writes "NO ADDRESS".
Why on earth would the sender feel the need to write "no address" at the foot of the letter? Probably because there was no envelope containing the address of the San Francisco Examiner.   

The scale on the left is slightly cut off, but the 3rd page measures approximately 10 inches in length.
If the Zodiac Killer had placed all three pages together, placing the 3rd page facing outwards on the top or bottom, then by folding the letters in the middle twice, the face of his communication would measure approximately 2.5 inches in height. The highlighted pink section would be the visible part of his communication, and where the address of the newspaper should have been written. But because he delivered it directly to the San Francisco offices, there was no need for an address - which is exactly what he wrote.

Does the hand-delivery of this letter tell us anything else about the Zodiac Killer, other than his eagerness for publication? The following is speculative and must be regarded as such.

The Zodiac letters have been heavily dissected to discover the likely home residence of the Bay Area murderer, and so we shall attempt to make some observations regarding this communication.

How prepared would the Zodiac Killer be, to travel a long distance just to hand-deliver this letter, rather than mail it?
If the Zodiac Killer lived or worked in San Francisco, then it isn't a problem to deliver it in person, either by making the journey specifically or en route to his workplace. However, if he lived in an outlying area (but didn't work in San Francisco) such as Napa (44 miles), Sacramento (94 miles), Santa Rosa (57 miles), Vallejo (29 miles), Oakland (9 miles), then how likely would it be for a person to travel these distances for no other purpose than the desire to hand-deliver a letter?  Surely, based on the 'least effort principle' of geographical profiling, the further away he lives, the less likely this would be the case   

This may suggest that the killer either lived and worked in San Francisco, or lived in one of these other regions and traveled into San Francisco for his profession. If he lived in Napa, for example, would he travel 44 miles (88 miles round trip) for the sole purpose of dropping off a letter, rather than mail it in Napa or somewhere close by? Unless, he lived in Napa and worked in San Francisco.

If the August 4th 1969 'Debut of Zodiac' letter was personally delivered by the murderer to the San Francisco Examiner, does it in some small way reveal something about Zodiac Killer and his likely residence, or is "no address" the likely outcome.     

In a previous article it was considered that the Zodiac Killer's identity was born on August 3rd 1969, but on this occasion I shall take an altogether different approach, and consider the possibility that the Bay Area murderer had already decided upon the pseudonym Zodiac when he mailed the trinity of letters and ciphers to the Vallejo Times-Herald, San Francisco Examiner and San Francisco Chronicle on July 31st 1969.
The San Francisco Chronicle letter (part 3) reads as follows "Here is part of a cipher the other 2 parts of this cipher are being mailed to the editors of the Vallejo Times and SF Examiner. I want you to print this cipher on the front page of your paper. In this cipher is my idenity. If you do not print this cipher by the afternoon of Fry.1st of Aug 69, I will go on a kill ram-Page Fry. night. I will cruse around all weekend killing lone people in the night then move on to kill again, until I end up with a dozen people over the weekend." The final 18 characters of the San Francisco Chronicle code remain undeciphered. However, the clues to breaking the remaining portion of the cipher may reside within the letters themselves. 
The 408 cipher message read "I like killing people because it is so much fun it is more fun than killing wild game in the forrest because man is the most dangerous animal of all to kill something gives me the most thrilling experence it is even better than getting your rocks off with a girl the best part of it is that when I die I will be reborn in paradice and all the (people) I have killed will become my slaves I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife. ebeorietemethhpiti."  The unbroken characters are shown in red.     

The murderer chose his words carefully, stating "in this cipher is my identity" rather than his name. This became evident when the vast majority of the 408 cipher was cracked a matter of days later, and the killer revealed "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife." This still left open the possibility that his identity or pseudonym was contained in the 408 cipher. The San Francisco Chronicle letter was the only one of the trinity that contained "in this cipher is my identity," so logically, one could conclude that the 18 undeciphered characters at its foot, was the location of the murderer's identity.
If the killer had already decided upon his pseudonym when he wrote the three July 31st 1969 letters, then his decision to begin all three letters with "This is the murderer" and "I am the killer" (twice) was deliberately engineered to withhold the pseudonym Zodiac from the letters. The reason being - it was concealed in the final 18 characters of the 408 cipher.
It could be argued, that if he was to reveal his identity or pseudonym in the 408 cipher, then logically he would sign off the cryptogram with it. This was also apparent in the 340 cipher, with the near-Zodiac tantalizingly placed on the final line. 
If the Zodiac Killer had revealed his pseudonym straight away, then one of the letters would have opened with "This is the Zodiac" rather than "This is the murderer" (exactly like the August 4th 1969 letter). The other two letters would have opened with "I am the Zodiac Killer" rather than "I am the killer". But the murderer and author of the letters wanted to hide his pseudonym for now, and conceal it in the final 18 characters of the 408 cipher.    

We can now complete the 408 message:
"I like killing people because it is so much fun it is more fun than killing wild game in the forrest because man is the most dangerous animal of all to kill something gives me the most thrilling experence it is even better than getting your rocks off with a girl the best part of it is that when I die I will be reborn in paradice and all the (people) I have killed will become my slaves. I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife. I am the Zodiac Killer."​
This is an attempt at reasoning a solution from within the letters themselves, and not a claim of a definitive solution 

THE 18 UNSOLVED CHARACTERS [PT2]
THE 18 UNSOLVED CHARACTERS [PT3]

Officer Richard Hoffman arrived at the Blue Rock Springs parking lot at approximately 12.13 am on July 5th 1969. Shortly thereafter, an ambulance was summoned (arriving at around 12.20 am), and removed the victims from the crime scene for the 10 minute journey to Kaiser Hospital, where Darlene Ferrin was pronounced dead upon arrival at 12.38 am. Here is an extract from page 7 of the police report:

'On initial arrival, RO requested by radio an ambulance & an investigation at the scene & upon returning to Officer Hoffman RO went to assistance of subject on ground, as Officer Hoffman was with a subject that was sitting on left front seat behind wheel that was also injured. This subject later identified as Darlene E. Ferrin, WF, 19, of 864 Beechwood. 
On preliminary examination of Mageau, it was apparent he had been shot a number of times, he had blood all over his face & blood coming from his mouth as well as his left leg with blood. RO felt it was necessary to question subject inspight of the fact the subject was in great pain. Subject was coherent & RO asked him, "do you know who shot you?" and he replied "no". RO then asked Mageau to give me some type of description & he replied that he can't. RO then asked a series of questions & was told by Mageau that the responsible was a white male, young & heavyset by himself & that he was in a brown vehicle. Questioning continued until the arrival of the ambulance. By this time Sgt's Rust, Lynch and Odiorne had arrived at the scene & RO gave them the information from the victim & gave a description over the air to all units' 

Michael Mageau also told Officer Hoffman that the perpetrator was last seen heading in the direction of Springs Road and Vallejo. By 12.20 am a rudimentary description of the perpetrator, his vehicle, and direction of travel had been given to all units, who likely scoured the area of Springs Road towards Vallejo. The killer couldn't be certain his vehicle wasn't spotted leaving the Blue Rock Springs parking lot and couldn't be certain that both Darlene Ferrin and Michael Mageau were dead, despite his proclamation in the 12.40 am payphone call to police dispatcher Nancy Slover. With multiple units searching for a description of the vehicle, how likely is it that, the killer parked his car outside Joe's Union gas station and made a telephone call to the operator and Vallejo Police Department - a police station situated in extremely close proximity to the payphone. He may have been under the impression that his crime had not been discovered at this juncture, but would it have been the sensible option to remain in his vehicle, with possibly blood transfer on his clothing and the gun still in his possession. If the killer did not have a residence nearby, then he had either driven around or parked up somewhere from midnight to 12.40 am- all while a police search of the area is unfolding around him. There is, however, a new and compelling argument to be had, that may dispel the idea of a killer making a payphone call while in the presence of his vehicle- and can be found in the police report and August 4th 1969 'Debut of Zodiac' letter.  

This is an extract from page 13 of the police report:
'7-5-69 A call received at 12.40 AM by unknown citizen "I want to report a double murder. If you will go 1 mile east on Columbus Parkway to the public park, you will find the kids in a brown car. They were shot with a 9 mm Luger. I also killed those kids last year. Good-Bye" 

'12.47 AM Mrs Johnson PT&T operator called. The above call was traced to a coin-operated telephone at Joe's Union, Tuolumne and Springs Road. The call was traced by Betty MAIN whose supervisor would not allow her to give a statement at this time.' 

This is the recollection of Nancy Slover in the 2007 Zodiac documentary, describing the latter part of the telephone call:
'But he said something like goodbye (drawn out in nature) and he hangs up, and I'm just kind of sitting there thinking "Oh my God."' 

Here is part of Zodiac's August 4th 1969 'Debut' letter:
'The man who told police that my car was brown was a negro about 40-45 rather shabbly dressed. I was in this phone booth having some fun with the Vallejo cop when he was walking by. When I hung the phone up the damn thing began to ring & that drew his attention to me + my car.'

These four sections of text should be enough to pour huge doubt on a killer making a telephone call to police, having driven to the payphone in a "brown car." Further bolstering the idea of a killer on foot, who lived nearby. The Zodiac Killer, in his own words, places his vehicle right next to the payphone. He corroborates this using the 'negro male', who spotted him and his vehicle when the phone rang as he hung it up. If the Zodiac Killer is in his vehicle as he claimed, it is highly doubtful that once he replaced the receiver he perched himself alongside his vehicle and smoked a cigarette for several minutes, with an eyewitness clocking him and his vehicle. He would have "hung the phone up," returned to his vehicle immediately and driven away. This sequence of events couldn't have taken much longer than 10 seconds.

Police dispatcher Nancy Slover, once the Zodiac Killer had hung up, contemplated the gravity of what she had just heard, likely finishing off writing details of the call, "kind of sitting there thinking "Oh my God." She then had to reconnect to the operator to discover the origin of the call - who would then have traced the call to Joe's Union on Springs and Tuolumne.
'Ringback' would have been used to 'dial' back to this payphone, thereby making it ring. Unless this sequence of events could be accomplished in less than 10 seconds using the technology of 1969, the Zodiac Killer would never have heard the phone ringing. He would have returned to his vehicle and been long gone. The ringing payphone was never reported in any newspapers, so the Zodiac Killer had to be within audible range to know of this occurrence. Nancy Slover received the phone call at 12.40 am, and the Zodiac spoke for approximately 30 seconds. The call would surely have ended before 12.41 am, yet, Mrs Johnson (PT&T operator) didn't get back to police, stating the call had been traced, until 12.47 am. That is just over 6 minutes later. If the trace and 'ringback' had occurred almost immediately (in under 10 seconds), why, bearing in mind the gravity of the murderous phone call, did it take 6 minutes to relay this crucial information to police.   

If the PT&T operator had contacted police the moment they had traced the phone call (12.47 am), then this operation would have taken several minutes. If this were the case, then the Zodiac Killer could never have heard the phone ring if he had driven away in his vehicle. If Joe's Union payphone had been rung in a reasonable estimate time of 30-60 seconds by PT&T operators- once Zodiac had hung up- he still wouldn't have failed to reach his vehicle and driven away. However, it is certainly possible he could have heard the payphone ring if he was on foot while walking away towards his residence. He would still be within audible range.

The Zodiac Killer would have rang the operator that morning and asked for the Vallejo Police Department- hence their ability to 'trace' the call. But, once the Zodiac Killer had 'hung the phone up', is it possible that Nancy Slover could finish up her written record of the call, sit there briefly, thinking "Oh my God," contact the PT&T operator, who then facilitated a trace on the call, and rang the Joe's Union payphone inside of the time it takes for Zodiac to reach his vehicle and drive away. If the 'ringback' took as little as 30-60 seconds, then it's highly likely the Zodiac Killer heard the payphone ring as he was walking away from the Springs Road and Tuolumne Street intersection on his way home. The 40-45, rather shabbily dressed, negro male now becomes the perfectly described eyewitness, who saw Zodiac in his "brown car by the payphone." What a helpful guy.
 

Many have toyed with the idea of a Zodiac Killer in Riverside, California, responsible for the murder of Cheri Jo Bates on October 30th 1966 or at the very least the author of the Confession and Bates letters. There are tantalizing threads in regards to the three Bates letters allying with his 'trinity' of communications mailed to the Vallejo Times-Herald, San Francisco Chronicle and San Francisco Examiner on July 31st 1969, just over two years later. The double postage was evident, and the threat of "more victims " was apparent in both. The April 30th 1967 Bates letters stated "Bates had to die, there will be more." The Vallejo Times-Herald communication carried a similar threat: "I will cruse around and pick of all stray people or coupples that are alone then move on to kill some more untill I have killed over a dozen people." 
It is also pointed out that the Zodiac Killer was responsible for the Bates letters because he signed off two of the letters with a Z-like alphabetical character. The Z representing Zodiac. The following will cast some doubt on this supposition and hopefully give us the exact date the Zodiac Killer first thought up his pseudonym Zodiac. In other words, the pseudonym Zodiac didn't exist for this individual in 1967 and therefore the alphabetical Z wasn't representative of Zodiac, or the precursor to it.​ 

On the right is an excerpt from the San Francisco Sunday Examiner and Chronicle dated August 3rd 1969. The Vallejo Police Chief Jack E Stiltz "urged the writer yesterday to send more letters with more facts to prove his connections with the crimes." The Bay Area murderer duly obliged with the 'Debut of Zodiac' letter, received by the San Francisco Examiner on August 4th 1969. It was called the "Debut" letter for good reason- it was the day the Bay Area murderer revealed his pseudonym to the world, opening with the now infamous line "This is the Zodiac speaking." But if Chief Jack E Stiltz had not requested more details, it is extremely unlikely this correspondence would have been mailed at all. We would have had to wait over two months until the October 13th 1969 Paul Stine letter for Zodiac to introduce his pseudonym into the public domain, if ever at all. 
The 'Debut of Zodiac' letter only existed because of Chief Jack E Stiltz- and this communication is the only reason our knowledge of the killer as Zodiac existed at this point in time. The choice of the pseudonym being revealed in this letter was not a choice made by the killer, because he wouldn't have written it, if not pressed into action by reading this newspaper column. 
In fact, the Zodiac Killer may never have existed under this name, if it wasn't for this publication by the San Francisco Sunday Examiner and Chronicle on August 3rd 1969. There is further evidence that the American public played a key role in igniting the killer's choice of pseudonym 
If the Z on the Bates letters really stood for Zodiac, then the murderer of Cheri Jo Bates, David Faraday, Betty Lou Jensen and Darlene Ferrin had almost three years to create an appropriate pseudonym before the July 31st 1969 'trinity' of communications proclaiming his collection of slaves for the afterlife. He had six and a half months from the December 20th 1968 double murder until the attack at Blue Rock Springs Park. He had 27 days from the July 4th 1969 attack until the mailing of the July 31st 1969 'trinity.'  This was his arrival to the world, yet he didn't sign off any of these letters with 'Zodiac' or even a 'Z'.
If he was surreptitiously operating under the name of Zodiac at this point, he clearly didn't give this impression when he opened up two of his communications with the rather unoriginal opening line of "I am the killer of the 2 teen-agers last Christmass at Lake Herman and the Girl last 4th of July" to the Vallejo Times-Herald and San Francisco Examiner. The San Francisco Chronicle was equally devoid of any pseudonym or initial, beginning with "This is the murderer of the 2 teenagers last Christmass at Lake Herman + the girl on the 4th of July near the golf course in Vallejo." 
The reason behind this, being that he hadn't formulated the pseudonym Zodiac at this juncture. The prompt was to come just three days later on Sunday August 3rd 1969- the day the 'Zodiac Killer' was born in the mind of the killer. 
The San Francisco Sunday Examiner and Chronicle opened with the lines "A self-accused killer failed to keep a threat of mass murder here, but there was no slackening of tension or mystery caused by the warning. The police department telephone system was clogged at times by anxious callers asking if the "cipher killer" had been caught."
The killer read this publication and was probably dismayed at the pseudonym of "cipher killer" attributed to him. He sat back in his armchair and was likely sparked into action to create his own pseudonym. He thumbed through the San Francisco Sunday Examiner and Chronicle of August 3rd 1969 during the day, until he arrived at the Zodiac horoscope page, and a light went on. This was the day the 'Zodiac Killer' was born.    

Inspired by the excellent feedback in comments, we will tackle the widely perceived notion that the murderer of five, known as the Zodiac Killer, enjoyed bragging and boasting about his four canonical crimes. The skepticism surrounding the brutal knife attack on Bryan Hartnell and Cecelia Shepard lingers- not only from the theatrical aspect of the crime- but from the evident lack of correspondence detailing his exploits by the lake. The Zodiac Killer (assuming the 340 cipher was not Lake Berryessa specific) did not mail any communication outlining the murder and attempted murder of the couple alongside the Knoxville Road. It will be argued, that the lack of communication boasting and detailing the Lake Berryessa crime, was not unusual in regard to the Zodiac. The Bay Area killer never willingly boasted or went into extensive detail about any of his first two crimes either.​ 

The Zodiac refrained from any communication after the December 20th 1968 murders, until three communications arrived six and a half months later to three newspapers.
There was no boasting about either Lake Herman Road or Blue Rock Springs. The killer simply provided details and 'evidence' he was the responsible.
"This is the murderer of the 2 teenagers last Christmass at Lake Herman + the girl on the 4th of July near the golf course in Vallejo 
To prove I killed them I shall state some facts which only I + the police know."
Christmass. [1] Brand name of ammo Super X [2] 10 shots were fired [3] the boy was on his back with his feet to the car [4] the girl was on her right side feet to the west. 
4th July. [1] girl was wearing paterned slacks [2] The boy was also shot in the knee [3] Brand name of ammo was western.
​The decrypted 408 cipher contained a rambling message, but made no direct reference to either of the first three murders. The details he did provide in the three letters, were only given as evidence that the author was indeed the killer. No facts about how each crime unfolded and how he terrorized the victims was given by the Zodiac Killer.
This probably would have been the end of it regarding the Benicia and Vallejo murders, but for Vallejo Police Chief Jack E Stiltz, who still expressed doubts regarding the author's claims. He specifically asked for the killer to contact the newspapers or police again. Chief Jack E Stiltz was less than satisfied that the letter writer and killer were one and the same, as detailed in an extract from the Saturday August 2nd 1969 San Francisco Chronicle. He requested the writer to send a second letter "with more facts to prove it." Another Zodiac article featured the following day on Sunday August 3rd 1969 in the San Francisco Examiner. Jack E Stiltz was "still not convinced the letters and codes were written by the actual killer.' The police chief 'urged the writer to send more letters, with more facts to prove his connections to the crimes."
The response by the Zodiac was swift, when the following day the San Francisco Examiner received the 'Debut of Zodiac' letter giving the police chief what he had asked for: "In answer to your asking for more details about the good times I have had in Vallejo, I shall be very happy to supply even more material." Without the prompt by Jack E Stiltz it is extremely likely this communication would never have been composed and sent to the newspapers. Our knowledge of the 'pencil flashlight', the supposed negro eyewitness or his recollection of the Mageau shooting would never have been known. In other words, he didn't willingly brag about the crimes, he was prompted into a response by the utterances of the Vallejo police chief.   
But for Jack E Stiltz, the Zodiac Killer may not have written from July 31st 1969 until October 13th 1969, when the Paul Stine letter arrived. In two and a half months the killer had murdered five people and attempted to murder two people, yet during this time period he would have likely written only two sets of communications. Not much of a braggart.
​Therefore, the fact the killer failed to write extensively about his Lake Berryessa exploits was not particularly out of character.

But for two phone calls taking credit for the second and third crime, he seemed rather less than forthcoming about detailing the mechanics of his murders unless prompted.
His murder of Paul Stine on October 11th 1969 was followed by a relatively short letter. It declared "I am the murderer of the taxi driver over by Washington St + Maple St last night, to prove this here is a blood stained piece of his shirt. I am the same man who did in the people in the north bay area."
He was once again supplying evidence he was the killer, just like the July 31st 1969 letters, but added no details whatsoever about the actual murder of the taxicab driver or his exploits in the taxicab.
He added a brief description about his venture into the park: "The S.F. Police could have caught me last night if they had searched the park properly instead of holding road races with their motorcicles seeing who could make the most noise. The car drivers should have just parked their cars and sat there quietly waiting for me to come out of cover." The inability of police to capture him was highlighted, but again, there was no maniacal boasting about the murder or extensive details regarding it. Then came the prompting once more. This time by Chief of Inspectors ​Martin Lee.  
Chief Martin Lee, speaking to the San Francisco Chronicle stated "His boast of being in the area we were searching while we were searching, it is a lie. We had the whole area flooded with lights. We had seven police dogs and a large number of patrolmen searching the area tree by tree and bush by bush. The dogs are the best in the country. A mouse couldn't have escaped our attention." link.  He added "The fact Zodiac failed to mention the dogs and floodlights proves he wasn't anywhere in the vicinity."  This last statement is patently flawed logic, because absence of evidence is not evidence of absence. This, coupled with the police stating Zodiac made mistakes, forced Zodiac into a response outlining details about the crime. Whether this was a cunning ploy by police to rile the Zodiac Killer into further communication and possibly trip himself up, or whether they really believed Zodiac never entered the park, can only be speculated. But it worked.

.On November 9th 1969 the Zodiac Killer mailed the 'Bus Bomb' letter, opening with the lines "I have grown rather angry with the police for their telling lies about me. So I shall change the way the collecting of slaves. I shall no longer announce to anyone. When I committ my murders, they shall look like routine robberies, killings of anger, + a few fake accidents, etc." Remember, Chief Martin Lee had called Zodiac a liar. 
However, not once did the Zodiac Killer brag or boast about the callous murder of Paul Stine. He reacted to the police claims, by retorting "2 cops pulled a goof, hey pig doesnt it rile you up to have your noze rubed in your booboos, the police don't have much to work on, as of yet I have left no fingerprints behind me contrary to what the police say, and I was leaving fake clews for the police to run all over town with."
The rest of his communication was reserved for the bomb he was allegedly constructing. The Zodiac Killer was full of threats, but so far hadn't willingly boasted about the very nature and details of his chilling crimes.
The final line of the 'Bus Bomb' letter is testimony to the agenda of the Zodiac Killer up to this point.
"To prove that I am the Zodiac, Ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves."  The Zodiac Killer was referring to the Vallejo cop Jack E Stiltz, who prompted the 'Debut of Zodiac' letter, asking for more details, and Zodiac did respond- informing Jack E Stiltz about his 'pencil flashlight' or electric gun sight. The 'Bus Bomb' letter was in direct response to Chief Martin Lee, to whom, he was trying to prove he did venture into the park and didn't leave any evidence at the crime scene. However, what is evidently lacking in this communication, is the lack of glorification in the murder or detailing of the actual crime itself. 
The Zodiac Killer was undoubtedly a ruthless and merciless killer, but as of November 9th 1969, the closest the Zodiac Killer came to boasting about the actual murders and attempted murders thus far, was when asked to do so.
He replied to Jack E Stiltz "I fired the first shot at his head, he leaped backwards at the same time, thus spoiling my aim. He ended up on the back seat then the floor in back thashing out very violently with his legs; that's how I shot him in the knee" and "All I had to do was spray them as if it was a water hose."
The 'Bus Bomb' letter may still have been mailed, but that is probably all it would have contained- details of his bus bomb and the threat of more murders, and likely little or no reference to the murder he had already committed. Had he wanted to provide copious material about the Paul Stine murder, he had every opportunity when he mailed the October 13th 1969 letter, but he refrained from doing so. The premise of the Zodiac Killer as somebody who enjoyed boasting about his crimes is not apparent in his writings, unless pushed. The threats however, would still continue.
The Zodiac Killer thought he had provided all the evidence required to prove he was the Lake Berryessa perpetrator, by writing on the car door of Bryan Hartnell's white Karmann Ghia and making the telephone call, yet it wasn't enough for some. Despite this being his most audacious crime to date, he again remained deafeningly silent on the specifics of the attack. Bryan Hartnell's survival and testimony of the crime, would inadvertently give the Zodiac Killer all the newspaper coverage of the actual crime he needed, if this was ever a requirement of the Zodiac Killer. 
Every correspondence to date, other than the extra details he was prompted into supplying, had one thing in common.

July 31st 1969: "If you do not print this cipher by the afternoon of Fry.1st of Aug 69, I will go on a kill ram-Page Fry. night. I will cruse around all weekend killing lone people in the night then move on to kill again, until I end up with a dozen people over the weekend."
October 13th 1969: "School children make nice targets, I think I shall wipe out a school bus some morning. Just shoot out the front tire + then pick off the kiddies as they come bouncing out."
November 8th 1969: "This is the Zodiac speaking. I though you would nead a good laugh before you hear the bad news. You won't get the news for a while yet. Could you print this new cipher in your frunt page ? I get aufully lonely when I am ignored, so lonely I could do my Thing."
November 9th 1969: "What you do not know is whether the death machine is at the sight or whether it is being stored in my basement for future use. I think you do not have the manpower to stop this one by continually searching the road sides looking for this thing. + it wont do to re roat + re schedule the busses because the bomb can be adapted to new conditions. Have fun!! By the way it could be rather messy if you try to bluff me. PS. Be shure to print the part I marked out on page 3 or I shall do my thing."
It was the threat of the crime itself, not the basking in the crime that had passed. The Zodiac Killer was prompted into ridiculing the police and supplying them with "more details" about the crimes, but terror was the 'thing' he enjoyed most.     

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'For 35 years starting in 1965, the San Francisco Chronicle and Examiner operated under a Joint Operating Agreement whereby the Chronicle published a morning paper and the Examiner published in the afternoon. The Examiner published the Sunday paper's news sections and glossy magazine, and the Chronicle contributed the features.' Wikipedia. 
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On August 4th 1969 the San Francisco Examiner received the 'Debut of Zodiac' letter, in which the killer revealed his pseudonym for the first time. This letter was not planned, as it was only mailed by the killer in response to an article released in the newspaper over the weekend, in which Vallejo Police Chief Jack E. Stiltz implored the murderer of three to supply more details about his crimes, to effectively prove that the author of the July 31st 1969 letters was in fact the killer. The Zodiac duly obliged. The first newspaper article was released by the San Francisco Chronicle on Saturday August 2nd 1969. Jack E. Stiltz requested the writer to send another letter "with more facts to prove it." The second newspaper article followed on Sunday August 3rd 1969 in the San Francisco Examiner. Jack E. Stiltz was 'still not convinced the letters and codes were written by the actual killer.' The police chief 'urged the writer to send more letters, with more facts to prove his connections to the crimes.'  The 'Debut of Zodiac' letter was hand delivered to the San Francisco Examiner the following morning, giving rise to the notion he is responding to the Sunday article in particular. This may be important if we analyze the nature of the communication and the actual paper it is written on. 

The Zodiac committed four attacks we know of. The first two at Lake Herman Road and Blue Rock Springs were perpetrated on a Friday in the hour preceding midnight. The Lake Berryessa and Presidio Heights attacks were perpetrated earlier, both on Saturday. This fed into the belief that Zodiac had a regular Monday to Friday, 9-5 job, with his Friday attacks likely committed closer to home due to time constraints, whereas on Saturday he could venture further afield, as it was one of his rest days. This may have come into play when the Zodiac delivered his August 4th 1969 letter.

​The Zodiac had just embarked on his letter writing campaign, when he mailed the 408 cipher on July 31st 1969, split into three sections of 136 characters and each mailed to three newspapers, the San Francisco Chronicle, San Francisco Examiner and Vallejo Times-Herald, all of which decided to publish. When Jack E Stiltz questioned the validity of the letter writer, Zodiac was eager to reply, shown by the fact his response was received on Monday morning, the day after the August 3rd 1969 Sunday Examiner article. He must have hurriedly drafted a response in order that his letter was published in the afternoon edition, but with one key difference.

The Zodiac Killer commonly used Eaton brand paper in his communications with the newspapers, but the 'Debut of Zodiac' letter was a notable change, using Woolworth's Fifth Avenue paper, suggesting he was thrown out of his normal routine. No doubt he kept a supply of Eaton paper at his residence, which he reverted back to after the 'Debut of Zodiac' letter. It seemed like the Woolworth's Fifth Avenue brand paper was a rushed buy, when he had no easy access to his home location, yet was still in a location to readily purchase the Sunday Examiner newspaper.. Here is one possible scenario, but obviously not the only one.

"The Zodiac Killer has just completed his 408 cipher and the weekend is approaching. He decides to use his Saturday and Sunday off work to relax and bask in his new found notoriety. If he is a resident of Vallejo or Benicia, then a thirty mile weekend trip away to San Francisco, may seem like a justified reward to enjoy his passion of theater in the Union Square and Tenderloin District. San Francisco may be an area he is already familiar with, if he works there. Then Jack E Stiltz puts a fly in the ointment by issuing a doubt that the killer and letter writer is the same person. The Zodiac Killer enjoying a cup of coffee over breakfast in his hotel getaway, picks up his paper and nearly chokes when he reads the article. Young and impulsive, his need to respond is immediate before Monday's edition. He finishes breakfast in his theater district hotel and heads to the nearest stationers to purchase some paper and a felt tip pen."  

"The first letter in which he christened himself "Zodiac" carried a different watermark than three earlier letters (Monarch-cut bond, imprinted with an Eaton watermark). The new watermark was fifth avenue, an imprint of Frank Winfield Woolworth's national chain. A huge Woolworth's stood just a block away from the Chronicle, at the cable car turntable at Fifth and Market and Powell. In the basement, next to the goldfish, Woolworth's sold blue felt-tip pens and paper exactly like Zodiac used. What if he bought his paper and blue felt-tip pens there?"  Robert Graysmith. 
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His Eaton paper was at his residence, but he is on a weekend trip. The easy option is to purchase a temporary pad of paper from the nearest location and Woolworth's would have been the obvious choice. It is in the heart of the theater district, just 10 minutes walking distance from Union Square and the Westin St Francis Hotel, the location where Zodiac was believed to have flagged down Paul Stine just two months later on October 11th 1969. Robert Graysmith highlights the Westin St Francis Hotel at Union Square, along with the Pinecrest Restaurant in his book 'Zodiac', whereas the article in the San Francisco Examiner on October 23rd 1969 stated "The search also took police to Nob Hill, where the Fairmont Hotel became involved again in the manhunt. This was because: Cabbie Paul Stine, 29, the Zodiac's latest victim is believed to have picked up his fare on a street near the famed hotel. A waitress in the hotel candy shop-fountain told police she served coffee during the television show (Jim Dunbar/Melvin Belli) to a man who resembled composite drawings of Zodiac. She saved the cup and saucer for a fingerprint check."
​
If Zodiac was a visitor to one of these hotels, then the footnote in his 'Debut of Zodiac' letter declaring "No address" may carry some irony. The Zodiac Killer would later send two further missives, the 'Little List' and 'Exorcist' letter, in which he featured the Gilbert and Sullivan satirical comedy, The Mikado, which played in the San Francisco theater district during this period. This location of Woolworth's, the theater district, the offices of the San Francisco Chronicle and San Francisco Examiner and the pick-up-point of Paul Stine on October 11th 1969, certainly center the focus on this small area of San Francisco. The San Francisco Chronicle at 901 Mission Street/corner of 5th, and San Francisco Examiner at 835 Market Street are key locations.   

The murder of Paul Stine on Saturday October 11th 1969 was thought to have originated from a pick-up-point, either at the Westin St Francis Hotel or the intersection of Mason and Geary Streets. The time would have been approximately 9.30-9.40 pm - so a theater production ending at this time may have provided a connection. Was the Zodiac Killer again on a weekend away, enjoying his passion for the arts, only this time murder was on the menu? However, this murder was a little different. If the killer, as suggested earlier, was not a resident of San Francisco, but a guest at a hotel somewhere in the theater district, then you would assume this murder was pre-prepared. Just like the 'Debut of Zodiac' letter that was received at the San Francisco Examiner on the immediate Monday to the article, so was the October 13th 1969 Paul Stine letter, containing the swatch of the taxicab driver's shirt. His response to both events was almost immediate, yet this time, knowing his murderous intentions, was prepared with pen and paper in advance.

The Zodiac Killer mailed the 'Exorcist' letter on January 29th 1974 in response to the San Francisco Chronicle article entitled 'Weird Goings on at the Movies,' authored by Paul Avery and published on January 11th 1974, detailing the audience reaction to the recently released Exorcist movie in 1973. The news report was from the Northpoint Theatre, located at 2290 Powell Street, San Francisco. The theater was located 3.4 miles from the Washington and Cherry Street intersection, where Paul Stine was murdered, and only 1.7 miles from the region of Union Square, where the taxicab driver picked up Zodiac.
​
If the Zodiac Killer was a regular visitor to the area of San Francisco's theater district, then the Northpoint Theatre, easily accessible from Union Square, may have saw the murderer through its doors at some point, although he appeared notably underwhelmed by The Exorcist, describing it as "the best satirical comedy that I have ever seen,"
​
​Does the change in writing material give us an insight into the Zodiac Killer's movements precedent to the 'Debut of Zodiac' letter, or is it simply a case of reading nothing into something.   

The negro male was supposedly never identified or mentioned in the Blue Rock Springs police report. Was the Zodiac lying about this encounter, as many people would argue, or was this a genuine encounter by the Zodiac Killer? Here we will run through some of the arguments.   

In the police report it stated a call received at 12.40 am by unknown citizen: "I wish to report a double murder. If you will go one mile east on Columbus Parkway to a public park, you will find the kids in a brown car. They have been shot by a 9 mm Luger. I also killed those kids last year.... Good-bye."

At 12.47 am Mrs Johnson PT&T operator called. The above call was traced to a coin operated telephone at Joe's Union, Tuolumne and Springs Road. The call was traced by Betty Main, whose supervisor would not allow her to give a statement at this time.

The Zodiac Killer called at 12.40 am and the call was traced inside of seven minutes, which is not possible with the technology of 1969. A caller had to be on the line a minimum of 15 minutes for a call to be traced. Although not completely  accurate, this was referenced in the Zodiac (2007) movie, featuring a clip of the Melvin Belli 'call to chat show,' when Belli was instructed "Pacific Telephone says you need to keep him on the line for 15 minutes."

​It is likely the word 'traced' is being used in the loose sense of the word, and they actually 'discovered' the call was made from Springs and Tuolumne. 

The answer may lie in Zodiac's wording at the top of the page, where he said "When I hung the phone up the damn thing began to ring & that drew his attention to me + my car."  Betty Main traced the call, but was not allowed to give a statement. This could have meant that what the witness had to say, contained sensitive material, having been kept under wraps at that particular juncture. If Zodiac was telling the truth and the phone rang almost immediately after he hung it up, this was not likely a coincidence. Was it possible, that although Zodiac hung up the receiver, the operator didn't and was able to ring back the payphone. This would not identify the specific location of the payphone, but if somebody had picked it up, the operator could ask the person on the other end to identify their location, ie; the negro male Zodiac identified as walking by. We know police officers were redirected from the Blue Rock Springs Park to the corner of Springs Road and Tuolumne Street, and it is here the witness to the phone call may have been interviewed. It is equally conceivable that the Zodiac Killer gave the payphone number to the operator when he was patched through to the Vallejo Police Department. Either way, the Springs and Tuolumne payphone was rang back by the operator.
  
​Michael Cole, author of Zodiac Revisited made some interesting points on the Zodiackiller.com forum:
"(1) The information from the letter is being given in direct response to a request for additional identity verification. The other information given in the same context appears to be truthful (mostly). Therefore, I believe Z is being honest in the conveyance of this information. 
(2) We know that Z changed his behavior when he made his call to the Napa PD about three months later. Instead of hanging up the phone, he set it down thus avoiding the possibility of a ringback. This behavior modification is consistent with an experienced-based learning regarding the described ringback; not to mention it just sounds like good police procedure to implement a ringback under these circumstances. Therefore, I suspect the ringback did happen as described. Perhaps Nancy will provide some additional insight on this front. I've already asked the question in the other thread.
(3) We know that Mike Mageau described the car as being brown. 
(4) As mentioned previously, Z's statement implies that he knows somebody told police that his car was brown. Although I don't have the reference, this clearly implies that the detail was published somewhere.
Given all of the above, I suspect that Z honestly believed that the described witness was the person who told police about his car. He apparently, quite reasonably, believed that MM could not have ascertained the color of his car. This left the witness as the most probable source. The fact that the witness was never identified seems to imply that he chose not to come forward or that he was unaware of law enforcement's desire to talk to him."        

The most likely answer is ring-back as Michael Cole suggests, which is how the call was 'traced.' Somebody may have picked up and given the operator the details he had just observed. This was alluded to by Zodiac who stated in the Debut of Zodiac Letter  "The man who told police that my car was brown was a negro about 40-45 rather shabbly dressed." It is likely this information was withheld from the police report - and why Betty Main's statement was not made public. Either, as Michael Cole stated "The fact that the witness was never identified seems to imply that he chose not to come forward or that he was unaware of law enforcement's desire to talk to him," or he was located by responding officers, but requested his anonymity be respected and why this information was kept off the record.
But the fact the location of the payphone was 'traced' seems to implicate third party information, in that ring-back alerted somebody to its location. However, that still leaves the question - if the negro male was interviewed, was he able to give any additional information regarding Zodiac's description, that was 'incorporated' into the police report, or did his description simply tally with Michael Mageau's and was therefore not included. Or did he simply get no viable description of the killer or his vehicle at all. Either way, as Michael Cole stated, the Zodiac Killer would not make the same mistake again in Napa on September 27th 1969.       

The Zodiac signed off the 'Bus Bomb' letter mailed on November 9th 1969 with the words "To prove that I am the Zodiac, ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves."  But to whom was the Zodiac referring. The answer is almost certainly Vallejo Police Chief Jack E. Stiltz, a native Vallejoan who first joined the police force in 1939 and oversaw many changes, including the new station located at 111 Amador Street, before retiring with health issues in 1970. Jack E. Stiltz died in 1974. 

The Zodiac sent three coded segments in three letters on July 31st 1969 to the San Francisco Examiner, San Francisco Chronicle and Vallejo Times-Herald, giving details of his first two crimes to prove he was the actual killer. However, the Zodiac Killer was still doubted, with Police Chief Jack E. Stiltz wanting further proof the killer and letter-writer were one and the same. This can be seen here in this extract from from the Saturday August 2nd 1969 San Francisco Chronicle. He requested the writer send a follow up communication  "with more facts to prove it."  

This story was featured again on Sunday August 3rd 1969 in the San Francisco Examiner (shown here on the left). Jack E. Stiltz was "still not convinced the letters and codes were written by the actual killer". The police chief "urged the writer to send more letters, with more facts to prove his connections to the crimes".
The Zodiac Killer's response was almost immediate, when he hand delivered the 'Debut of Zodiac' letter just one day later, on August 4th 1969 to the San Francisco Examiner, to leave you in no doubt he was replying directly to Jack E. Stiltz. The Zodiac's opening gambit was "In answer to your asking for more details about the good times I have had in Vallejo, I shall be very happy to supply even more material. By the way, are the police having a good time with the code? If not, tell them to cheer up; when they do crack it, they will have me". He went on to describe the Blue Rock Springs Park and Lake Herman Road attacks in much greater detail and effectively informed Jack E. Stiltz about his attached gun sight;  "What I did was tape a small pencel flash light to the barrel of my gun. If you notice, in the center of the beam of light if you aim it at a wall or ceiling you will see a black or darck spot in the center of the circle of light about 3 to 6 inches across. When taped to a gun barrel, the bullet will strike in the center of the black dot in the light. All I had to do was spray them as if it was a water hose; there was no need to use the gun sights. I was not happy to see that I did not get front page coverage". 
​  
Fast forward to Presidio Heights on October 11th 1969 and Chief Inspector Martin Lee's claims that Zodiac "has made some mistakes." They did not believe that Zodiac could have been hiding in the park. Chief Inspector Martin Lee stated "His boast of being in the area we were searching is a lie. We had the whole area flooded with lights. We had seven police dogs and a large number of patrolmen searching the area tree by tree and bush by bush. The dogs are the best in the country. A mouse couldn't have escaped our attention."They also irked the Zodiac by claiming he had left fingerprints on the interior and exterior of the taxicab, particularly the blooded fingerprints on the driver side door panel.

Zodiac again felt compelled to reply in the November 9th 1969 'Bus Bomb' letter: "I have grown rather angry with the police for their telling lies about me...... p.s. 2 cops pulled a goof abot 3 min after I left the cab. I was walking down the hill to the park when this cop car pulled up + one of them called me over + asked if I saw anyone acting suspicious or strange in the last 5 to 10 min + I said yes there was this man who was runnig by waveing a gun & the cops peeled rubber + went around the corner as I directed them + I disappeared into the park a block + a half away never to be seen again", and again asked for newspaper coverage similar to the 'Debut of Zodiac' letter by threatening more attacks: "By the way it could be rather messy if you try to bluff me. PS. Be shure to print the part I marked out on page 3 or I shall do my thing. To prove that I am the Zodiac, Ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves".

The last time the Zodiac Killer was doubted, he supplied extra details of the Blue Rock Springs and Lake Herman Road attacks to Vallejo Police Chief Jack E. Stiltz, including his "small pencel flash light". He would repeat this in the Bus Bomb Letter, reminding everybody that he most certainly was the Zodiac Killer. In other words, to not doubt him and "Ask the Vallejo cop about my electric gun sight which I used to start my collecting of slaves". The Vallejo cop he is referring to, is Jack E. Stiltz. The Vallejo cop, to which he sent details about his improvised gun sight in the 'Debut of Zodiac' letter only three months earlier. He proved to Jack E. Stiltz that he was both the letter writer and the killer, and again here, in the Bus Bomb letter, he is referring back to this Vallejo cop - and to not doubt him again.