It has been widely considered that the Exorcist letter mailed on January 29th 1974 may have been the final correspondence from the infamous Zodiac Killer. But is its claim of 37 murders, if indeed this is what was meant, a realistic one. Firstly, we will take the unusual step of acknowledging the Zodiac Killer at his word, when throughout his campaign of terror he constantly informed the authorities of his murder count, displayed on each subsequent letter or card. But how accurate were his claims, and could a timeline of potential Zodiac victims be attributed to the periods in between each correspondence, bearing in mind that his declaration of seven murders on the Dripping Pen card of November 8th 1969 could be attributed with almost complete accuracy, albeit the missing murders in August, has still yet to be fully resolved. As stated previously, the months displayed at the foot of the Dripping Pen card could indicate the murder of David Faraday and Betty Lou Jensen in December, Darlene Ferrin in July, Cecelia Shepard in September, along with Paul Stine and Cheri Jo Bates in October. This meant six murders possibly attributed and one unaccounted for, due to his proclamation on November 8th 1969 indicating a total of seven victims up to this point.

So let us examine the period from this letter to the next confirmed Zodiac correspondence on December 20th 1969, that of the Melvin Belli letter, claiming he may lose control and claim a ninth and tenth victim. The suggestion of a search for a ninth and tenth victim, by inference, meant he had already claimed his eighth murder victim and it must have occurred between November 8th 1969 and December 20th 1969. So who was the most likely Zodiac victim, based on age, locality and nature of the crime during this time period. One possibility is Betsy Aardsma, murdered in the campus library of Pennsylvania State University on November 28th 1969 - although this crime has a number of question marks, including the locality - seemingly out of kilter with what we know of the killer to this point. There is, however, another interesting case that deserves closer scrutiny.          

Incidentally, a woman's body was discovered next to Paradise Drive, Belvedere, Tiburon in December 1966 - although the body, wearing a red dress had lain undiscovered for approximately three to four months, according to Marin County detectives. Also on December 1st 1969, Elaine Davis (17) disappeared from from her home in Walnut Creek, Contra Costa County, California. She was abducted during the evening hours through a sliding rear window. Two and a half weeks later on December 19th 1969 her body was discovered floating off  Light House Point, Santa Cruz, California, however, due to investigators misinterpreting the age of the victim at the time, her identity was only realized 31 years later when officials exhumed the body in 2000.
No link was ever ascertained between the murder of Elaine Davis and Leona Roberts, however, both victims fell within the correct age, area and timeline of the Zodiac Killer.    

On March 22nd Kathleen Johns was abducted and taken on a terrifying journey by an assailant she later claimed to be the Zodiac Killer. Even the Zodiac himself claimed his involvement, when he mailed a letter to the San Francisco Chronicle on July 24th 1970. There were many murders and disappearances in California during the month of March, including Cosette Ellison on March 3rd, Patricia King on March 5th, Judith Hakari on March 7th, Marie Anstey on March 13th and Eva Blau on March 20th. However, the 'My Name is...Letter' and Bus Bomb Diagram claimed 10 murders on April 20th 1970, with the Melvin Belli letter on December 20th 1969 indicating that 8 murders had taken place. If we therefore take the Zodiac at his word, only two murders had taken place in this four month period. If John Hood and Sandra Garcia were Zodiac victims, then none of the disappearances and murders in March were anything to do with the Zodiac Killer. On the other hand, if the Hood and Garcia murders were not Zodiac victims, then only two of these victims in March remain a possibility, not more. Unless for some reason only known to the killer, he committed more murders, yet failed to attribute them to himself. 

Moving forward two months to the Button letter on June 26th 1970, the Zodiac claimed 12 murders. He also stated he had "shot a man sitting in a parked car with a .38". The only event that tallied with the Zodiac's claim was the murder of police officer Sgt Richard P. Radetich (25) on June 19th at 5:25 am, who was gunned down by three shots from a .38 caliber revolver at point blank range through the driver side window of his vehicle while in the process of serving a parking ticket. He was seated in his police car by 643 Waller Street, when it is believed another vehicle pulled alongside and an occupant opened fire. Officer Richard Radetich would die 15 hours later. However, the Zodiac Killer, who almost always gained extreme pleasure from his mockery towards the police and authorities, only referred to his victim in the Button letter as a 'man', apparently failing to capitalize on the situation. This appears to shed reasonable doubt that he was responsible for the murder of Sgt Richard Radetich, although the caliber of the weapon was correct. 

The disappearance of Donna Ann Lass (25) from the Sahara Tahoe Hotel on September 6th 1970 seemed to push the Zodiac's murder count to 13, with the Halloween card mailed on October 27th 1970 proclaiming a possible fourteenth victim, arriving just two days after the murder of Nancy Bennallack (27), a court reporter, on October 25th 1970. Nancy Bennallack had been slain in her own apartment on Arden Way and Bell Avenue, Sacramento , cut down by over 30 knife wounds, indicating the severity of the brutal murder - although she had not been sexually assaulted. The crime scene indicated that the killer may have used tape to mask over his fingertips during the attack.  

Finally, onto the Los Angeles letter, mailed on March 13th 1971, where he laid claim to an estimated 17 or more murders.
In this letter he stated "I do have to give them credit for stumbling across my riverside activity, but they are only finding the easy ones, there are a hell of a lot more down there". He was apparently referring to the fact that detectives had forged a link between the Zodiac Killer and the senseless slaying of Cheri Jo Bates in Riverside on October 30th 1966, claiming there were many more victims in that region. 

One such attack, was the Robert Domingos (18) and Linda Edwards (17) double murder on June 4th 1963. The young couple were gunned down on a beach near Tajiguas Creek, Lompoc, Santa Barbara County. The killer had initially attempted to bind the couple, reminiscent of the Lake Berryessa Attack on Bryan Hartnell and Cecelia Shepard on September 27th 1969. But clearly, if the Zodiac was responsible for this couple's murder, along with Cheri Jo Bates, then his murder total should have read 8, by the mailing of the Dripping Pen card on November 8th 1969, which clearly it didn't. The suggestion of "there are a hell of a lot more down there", seems to conflict with his declaration on the Dripping Pen card of seven murders. The only reasonable explanation being, that these murders were not committed under the Zodiac umbrella. A pseudonym he would only adopt just prior to the 'Debut of Zodiac' letter, received by the San Francisco Examiner on August 4th 1969. The killer may have belatedly attached the 1963 murders of Domingos and Edwards, and the Riverside murder of Cheri Jo Bate to the Los Angeles letter claiming 17+ murders. This may explain the increase from the 14 victims claimed in the Halloween card approximately five months earlier. 

The murder of Cheri Jo Bates outside the Riverside City College library on October 30th 1966 may have been the day the Zodiac Killer, under this moniker, started his campaign of terror. However, it would be at least one month before his typed 'Confession' letter surfaced on November 29th 1966 with the threat of more to come. Five months later, on April 30th 1967, a further three letters sent to the Riverside Police, Riverside Press Enterprise and more chillingly, Cheri Jo Bates father, suggested that this killer was not going to stop anytime soon. At least two of the three April 30th Bates letters were signed off with what looked like a Z symbol, but at this juncture the authorities were a long way from finding out that this may have been the very beginnings of the infamous Zodiac Killer - the 'calm' before the storm of Lake Herman Road and beyond.

What, if anything, lies within the 'Confession' letter to suggest this declaration of murder was in any way related to the other crimes that began on December 20th 1968, just over two years later. It has been previously pointed out, that the author of the 'Confession' letter used the wording "She squirmed and shook as I choaked her. And her lips twiched". This having striking similarities to the 'Little List' letter mailed by the Zodiac Killer mailed on July 26th 1970, in which he stated "Some I shall tie over ant hills and watch them scream + twich and squirm." But more apparent, is the egocentric nature displayed in the 'Confession' letter, that he maintains throughout his correspondence to the authorities, right through to the Exorcist Letter mailed on January 29th 1974, revealing character patterns of his own unique writing style. In the 'Confession' letter his extreme use of the word 'I' appears no less than 19 times, along with his use of 'me', 'my' or 'mine' a further 12 times in this short letter comprising of 423 words. So, in total, a reference to himself appears no less than 31 times. That is 7.33% of the time, or once every 14 words - and something we were going to get accustomed to over the following eight years.

The 'Bus Bomb' letter, 'Little List' letter and 'Melvin Belli' letter are further examples of the Zodiac Killer's compunction to constantly refer to himself as the focus of attention within his writings. In the Melvin Belli Letter this occurs 16 times within the body of text, containing 134 words (11.94% of the letter). The 'Little List' letter contains 12 in 178 words (10.07% of the letter) and the 'Bus Bomb' letter is equally high in frequency.   

The Zodiac Killer mailed the 'Los Angeles' letter on March 13th 1971 and claimed "I do have to give them credit for stumbling across my riverside activity, but they are only finding the easy ones, there are a hell of a lot more down there." This may or may not be the case, but the murder of Cheri Jo Bates on October 30th 1966 is a crime, that in many respects, has the hallmark of the Zodiac Killer stamped all over it.