His four confirmed attacks were Lake Herman Road on 12.20.68, Blue Rock Springs 7.4.69, Lake Berryessa 9.27.69 and Presidio Heights 10.11.69. These four attacks were committed on a Friday, Friday, Saturday and Saturday respectively, all at the weekend, suggesting the killer may have had a standard 9-5 occupation from Monday to Friday, only committing his murders prior to a day of rest. Serial killers often begin their crimes close to home in what is termed a comfort zone. In other words, areas that are familiar to them, such as their leisure zones, their place of work, the location of friends and family, along with functional activities. But not too close to risk identification or draw attention to their home residence. Once a crime has been perpetrated, the main objective of the criminal is to return home or to relative safety. Killers will venture further away from their home base as they gain confidence, but generally not too far, as the least time they are traveling carrying the 'smoking gun' or harboring transfer from the crime scene, the better.
If he worked standard occupation hours and finished work on Friday at 5:00 pm, the least effort principle would come into play. Murder was on his mind, but having arrived home late afternoon or early evening, he conceivably wanted to travel the least distance possible, while still maintaining a reasonable buffer zone to his residence.
His Saturday crimes of Lake Berryessa and Presidio Heights were considerably further - and being a rest day for the Zodiac Killer - the least effort principle would be mitigated. Now we will examine the possible movements of the Zodiac Killer after each crime to narrow down a location for his home residence.
Eyewitness testimony from the Lake Herman Road murders suggested a very small window of time that the Zodiac Killer had available to him in order to escape detection, but one eyewitness, that of Stella Borges, was the most crucial of all. A second eyewitness, James Owen, passed the turnout at what was calculated to be 11:14 pm and he saw no victims lying on the turnout floor. However, Stella Borges in a revised timeline, passed the turnout at approximately 11:20 pm and saw both victims David Faraday and Betty Lou Jensen lying on the gravel turnout. Based on this chain of events, the earliest the Zodiac Killer could have murdered the young couple and started to leave the turnout would have been 11:15 pm. Stella Borges, it was estimated left her ranch at 11:15 pm heading towards Benicia. She reported passing no vehicles en route. Therefore the Zodiac Killer could not possibly have headed towards Vallejo along Lake Herman Road using this timeline. The only possible scenario using these claimed times, is the Zodiac Killer headed in an easterly direction towards Benicia and towards the relative safety of home.
After committing two brutal murders, possibly covered in biological material from the close contact murder of David Faraday, the sound of at least ten shots on a still dark night, and almost certainly still in possession of a .22 weapon, it would have been unimaginably stupid - and furthermore made little sense - for the killer to head in the opposite direction to his home residence, thereby risking a prolonged period of detection, and in all likelihood, ruling out Vallejo as the home residence of Northern California's most elusive serial killer.
The attack at Blue Rock Springs was approximated no later than 12:04 am on the 5th July 1969, however, the call the Zodiac Killer made to police dispatcher Nancy Slover at the Springs Road and Tuolumne Street payphone was logged at 12:40 am. This payphone was located only a 10 minute drive from Blue Rock Springs. So what had the killer done during this time period? It is highly unlikely he would have sat stationary in his car in the area, or outside the payphone for any prolonged period of time. After gunning down two people only 3.7 miles away, this would only have increased his risk of capture. The Zodiac Killer had likely planned this phone call to police in advance of the crime, despite the fact it carried greater risk. The payphone may have been chosen because it was known to the killer and not too close to where he lived.
In the phone call to police dispatcher Nancy Slover, the killer would announce his campaign of terror "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".
His final confirmed murder was that of Paul Stine at Presidio Heights on October 11th 1969. This was in stark contrast to his previous attacks, taking place in a built-up area with high risk. To commit such a brazen attack in a heavily populated location seemed on the face of it an unusual choice, which led to the idea the killer was very confident in these surroundings. It is well documented that a large proportion of his mailed correspondence was postmarked San Francisco, indicating he may have likely worked in San Francisco, yet lived in the Vallejo or Benicia region.