Covered extensively in previous articles, had the Zodiac Killer worked a conventional Monday to Friday, 9 to 5 profession and had lived in the Vallejo area at the time of his murders, we would expect to see his first two Friday attacks relatively close to his home base. Unconstrained by time on Saturday, the Zodiac Killer would be able to venture further afield for his attacks - which is exactly what happened. However, we now have another tool in our arsenal, highlighted in this short but informative video by BCU professor Craig Jackson. Here is a small extract: "Wherever the Yorkshire Ripper was based, the time of his murders would be a vital clue to where he lived. So, if one of the Yorkshire Ripper's victims was murdered in the early evening, 8 o' clock or 9 o' clock at night, that individual could be based very far away from where the Yorkshire Ripper's base was. But if the victim was murdered in the very small hours, midnight, or one or two in the morning, that victim would probably be very close to where the Ripper's base was, assuming that the Ripper would have to be home at a reasonable time to be with their partner or families, or friends who they lived with". The type of victim targeted, the areas they frequented and their availability also has to be factored into the target backcloth. Therefore, we will use the Zodiac Killer's four attacks and see if they conform to a home base in Vallejo.
If we apply the model of professor Craig Jackson to our killer, then an attack at approximately 11:15 pm at Lake Herman Road and midnight at Blue Rock Springs Park, would suggest a killer who lived close by and was aiming to return home sometime in the late evening to early morning hours. If the Zodiac Killer had lived near to the Springs Road and Tuolumne Street payphone, he would have arrived home at around 11:30 pm on 12/20/68, and 12:15 am on 07/04/69. The Zodiac Killer's attack at Presidio Heights would not have been affected by a "hit and miss" targeting technique. Had the murder of taxicab driver Paul Stine been planned ahead of time, he would know where he was to find his victim, where he was going to murder the taxicab driver and where his escape route lay before him - including his journey time back to Vallejo. Paul Stine was murdered shortly before 10:00 pm on 10/11/69. The Zodiac Killer (had he parked his vehicle near the Presidio Park) would have about 5-15 minutes of walk time, followed by a 50 to 60 minute journey home via the Golden Gate Bridge. At the latest, he would arrive home at approximately 11:15 pm. Therefore, his window of time to arrive back at his residence after three of his attacks, would fall within one hour of each other (between 11:15 pm and 12:15am) - although it may be slightly more.
The Presidio Heights area must also have been familiar to him, to risk such an audacious attack in a built-up area of San Francisco. Dr. Kim Rossmo summed it up perfectly: "The San Francisco murder differs significantly from the Zodiac's other crimes. Up to this point he was hunting in locations that had a good probability of containing his desired victims. Target selection was a function of area, not of an individual. However, it is unlikely the Zodiac was successful in all his searches; serial killers typically engage in extensive hunting activities, and for every attack there are many unsuccessful search attempts. In San Francisco, however, the Zodiac controlled the situation through his selection of victim type. The need for such control could be indicative of the distance the Zodiac had to travel to the crime site. Criminals who travel longer distances to offend are less likely to use uncertain target selection techniques".
His familiarity with Lake Berryessa (09/27/69) was also obvious. The Zodiac Killer knew on this occasion that a targeted attack in the late evening hours (close to midnight), similar to Lake Herman Road and Blue Rock Springs Park, was wholly uncertain with respect to finding a suitable victim or victims in this location. But he knew that a late afternoon or early evening attack within the expanse of Lake Berryessa, would be the safest bet, The location, on this occasion, effectively governed the earlier attack time. When this constraint was unburdened during his first, second and fourth attacks (assuming he lived in Vallejo and went directly home), his arrival time to his residence would have always fell within a 60-75 minute window of time. If the Zodiac Killer had a preconceived time he wanted to return home by, then Vallejo by the payphone was a perfect fit for a good night's sleep - as well as not arousing suspicion - had he been married (with children).