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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On August 4th 1969 the San Francisco Examiner received the 'Debut of Zodiac' letter, in which the killer revealed his moniker for the first time. This letter was not planned, 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 was featured asking the murderer of three to supply more details about his crimes, in essence to prove that the author of the July 31st 1969 letters was in fact the killer. The Zodiac duly obliged.
'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.  
The first newspaper article was released by the San Francisco Chronicle on Saturday August 2nd 1969. Jack E Stiltz requested the writer to send a second 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 received by the San Francisco Examiner the following day, so it is likely 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 sent 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, 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 very fact his response was received on Monday, 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 Monday edition, but with one key difference.
The Zodiac Killer used Eaton brand paper in his communications with the newspapers, but the 'Debut of Zodiac' was a notable change using Woolworth's Fifth Avenue paper, as though he was thrown out of his 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 seems 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.' Enter Robert Graysmith.                   

"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?"  
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."
Ironically Zodiac, if a visitor at one of these hotels, would add a footnote to his 'Debut of Zodiac' letter declaring "No address".
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-planned, with a vehicle or three mile walk back to Union Square.
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 Paul Stine letter, containing the swatch of the taxicab driver's shirt, on October 13th 1969. His response to both events was 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 Washington and Cherry Streets, the 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, the Northpoint Theatre, easily accessible from Union Square, likely saw the murderer through its doors at some point, although he appeared notably underwhelmed, 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 called at 12.40 am and the call was traced inside of seven minutes, 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 factually 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 mean, 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 responder 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. 
​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 and is how the call was 'traced.' Somebody picked up and gave operator the location of the payphone. 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 alluded "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 not included. Or did he simply get no viable description at all. Either way, as Michael Cole stated, Zodiac 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 could very well be 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 the first two crimes to prove he was the actual killer. The Zodiac Killer however was still questioned and Police Chief Jack E Stiltz still wanted more proof, as can be seen here in this extract from from the Saturday August 2nd 1969 San Francisco Chronicle. He requested the writer to send a second letter "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 is '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 swift when he mailed 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 replacement 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 police claims that Zodiac could not have been hiding in the park and had left fingerprints on the interior and exterior of the taxicab, particularly the blooded fingerprints on the driver side 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 press coverage similar to the 'Debut of Zodiac' Letter,  "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 was doubted he supplied extra details of the Blue Rock Springs and Lake Herman Road attacks to Vallejo Police Chief Jack E Stiltz and he again did the same in the Bus Bomb Letter, reminding everybody that he indeed was the Zodiac Killer. In other words do 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.