Canter and Young noted from a geographical standpoint that a commuter's crimes will generally be grouped closer together, whereas a marauder's crimes will be more spread. If the Zodiac Killer was a commuter living in Vallejo, one could expect him to commit multiple attacks at a secondary location such as San Francisco, in an attempt to focus the investigation far from home. Grouping the attacks within San Francisco would achieve this objective, but spreading the attacks would effectively nullify this tactic. A killer living in Vallejo may attempt to spread his attacks in all directions with each subsequent attack, designed in such a fashion to confuse investigators trying to pinpoint the murderer's anchor point, but may in essence have the reverse effect to the one desired. However, there is one important dichotomy to unpick when we consider the Zodiac Killer compared to most serial murderers - and that is the copious communications he mailed primarily from San Francisco.
His attacks took on the appearance of a marauder, while his letter writing took on the appearance of a commuter - which is exactly what he would have been, had he worked in San Francisco and lived in Vallejo. When your letter writing count outweighs your murder sites five to one, it is far easier to use this in order to focus investigators into a belief that you live in San Francisco, when it requires no more effort than traveling to work each day. The final confirmed murder at Presidio Heights could have been a deliberate choice by a killer determined to divert the investigation down a path far from home, but by reverse psychology, may have achieved the complete opposite to the one intended.
The Zodiac Killer showed his ability to be unconstrained by a method of operation or modus operandi, with the 'couple killings' more a result of circumstance than choice. Had a third person been present in either vehicle at Lake Herman Road and Blue Rock Springs Park, does anybody believe that the Zodiac Killer would have turned around and gone home? The same could be said for a single person. This was evident when the Zodiac Killer mailed his trinity of letters on July 31st 1969, stating "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". His other two letters made no mention of couples. The idea that this was a sexually frustrated hater of courting couples is not warranted by the limited number of attacks in the sample size, and the idea that he would have just skulked off home, disappointed that he didn't see any couple's making out, is a hard argument to sell. However, the notion of earlier attacks carrying less risk and distance in respect to a home residence, has statistically been proven in previous studies of serial killers, whether or not it is true in this instance.