The Zodiac Killer

The Lake Berryessa attack offered several examples of odd behavior on the part of the Zodiac.  There is, for instance, the four-cornered hood that he put on just before approaching the couple: its design is rare, if not unique, and the killer made no attempt to explain it either to the students or to the press. Presumably, he wished to conceal his identity, but this could have been accomplished less ostentatiously with a ski mask or similarly common item.  As a reason for attacking Shepard and Hartnell, he had a fabricated story about escaping from prison in the northwest, yet signed the car door with his easily recognizable crossed-circle logo and murder chronology.  It should be noted that he omitted from this chronology the Riverside murder, which was not attributed to him until 1970, leading many to view this omission as evidence that the Zodiac was not, in fact, responsible for the murder of Cheri Jo Bates.  He told the students that he wanted their money and car keys, but took only Hartnell's pocket change and left the keys and the girl's wallet on the picnic blanket, and tied them up and stabbed them rather than simply shooting them with the pistol he had pointed at them earlier.  Finally, he never took credit for this attack in a letter as he had for the Vallejo and San Francisco attacks.

The FBI's Crime Classification Manual describes three forms of offender behavior at the crime scene.  "Modus Operandi" is defined as the actions necessary to commit a crime and ensure a successful escape.  The two Vallejo attacks, for instance, show a consistent blitz-style MO using a handgun and followed by a quick, controlled retreat. The MO at Lake Berryessa is superficially closer in style to the Riverside attack, which was executed with a knife and preceded by some kind of verbal interchange between killer and victim, but the differences are apparent on examination: Bates' killer was ill-prepared for his attack, using only a small pocketknife on a young woman who fought back vigorously, whereas the Zodiac went to great lengths to immobilize his victims at the lake.  In fact, it seems that the man who killed Cheri Jo Bates wasn't even sure that he would kill her, having conversed with her for over an hour before he lost control and stabbed her -- at Lake Berryessa, there can be little doubt as to the Zodiac's intentions.  Modus Operandi is learned, pragmatic behavior, and can be improved upon with experience, as shown by the foresight evinced by the killer when he foiled a potential call-back from the Napa police switchboard by leaving the phone off the hook.  The Zodiac also became more audacious in attacking at dusk in an open area, though he was careful to choose one that was fairly isolated.  Willful alteration of the crime scene in order to confuse or mislead investigators is called "staging," and is usually seen in cases where the killer and victim are acquainted with one another: oftentimes, the offender will attempt to make the crime appear to be a random rape or robbery gone wrong.  This phenomenon does not seem present in the Zodiac case, unless one counts the letters as a form of staging, having been deliberately crafted to give an impression of their author as a dyslexic Gilbert and Sullivan fan. Any action taken by the offender that is unnecessary to the crime's completion, or is performed solely to gratify his own psychological needs, is called "personation."  The elaborate hood, the jailbreak lie and the demand for money and car keys are examples of personation. Repeated examples of the same personation by the same offender are called a "signature," and this occurred both clinically and literally on the car door: the crossed-circle design appeared at the foot of every letter from the Zodiac between 1969 and 1971. The phone call was another aspect of the signature, mirroring calls made to police in Riverside and Vallejo, and totally unnecessary to his escape. 

The killer's choice of the knife over the pistol, in conjunction with his use of the unusual hood, is generally cited as evidence that the Berryessa attack was one of ritual significance to the killer.  This may be true -- the hood remains unexplained except insofar as it was probably meant to instill terror in his victims, and by Hartnell's account the Zodiac seemed to lose control during the assault on Shepard.  However, the fact that he had this time chosen a location as open as the lakeside may have led to the tactical decision to use the knife, a silent weapon perhaps brought along for such a contingency.

There are some who remain unconvinced that the Berryessa attack was an authentic Zodiac incident, citing numerous deviations from the general pattern of the other Bay Area attacks.  There is, in truth, no conclusive evidence tying the Zodiac to this incident as there is for the Vallejo and San Francisco murders.  The handwriting on Hartnell's car is identifiably similar to that in the Zodiac's letters, but the door-writer's posture rules out a definitive authentication by the layman.  Regardless, the differences between the lakeside incident and the other Bay Area attacks -- which include the time of day, the lingering, the weapon, and the absence of a follow-up letter offering proof of the author's culpability -- are to most investigators outweighed by the circumstantial evidence of similar handwriting, weight, and general description, not to mention the phone call after the incident.  Behaviorally, the variations in MO and signature can be ascribed to the growing boldness, calculation, and self-gratification of a developed serial killer.  Moreover, if the true Zodiac were not in fact responsible, his drive for publicity would almost certainly compel him to deny the charges or offer a false confirmation as he did for the Riverside murder of Cheri Jo Bates.  A Zodiac copycat at Lake Berryessa would have to have been the right height and weight; he would have had to study and superbly forge the killer's handwriting; and he would have had to exhibit an understanding of the killer's need for situational control, at the same time being careful to leave none of his own personation at the scene.  Meanwhile, the true Zodiac would have had to suppress his most identifiable character trait.  While intriguing, this hypothesis requires a suspension of disbelief that is simply too great for most investigators.