There are many things to consider when using geographical profiling to narrow down an offender's home location, but on this occasion we will resort to basics. The 'least effort principle' is whereby people - in our case the Zodiac Killer - when faced with two or more alternatives with his decision making, will often opt for the one requiring the least effort . In terms of the Zodiac Killer, had he lived in Benicia and knew that young couples frequented the Lake Herman Road turnout, as well as Blue Rock Springs Park, and given that couples are available at both locations on any given night, he will choose the one nearest to his home. However, he will observe a 'buffer zone', described as an area around an offender's home residence that he will not operate, for fear, not only of being recognized, but drawing law enforcement onto his doorstep. For example: If the Zodiac Killer lived in Hastings Drive, Benicia, his buffer zone may be 6 miles by road or as little as 2 miles as the crow flies. See here. A serial killer usually begins his crimes close to home, somewhere he is familiar with, before he eventually gains in confidence and ventures further afield. So, if the Zodiac Killer lived in Benicia, he would use the 'least effort principle', 'buffer zone' and victim pool to select his first attack.
A recent survey in Germany studied the locations of serial killer victims in respect to the killer's home residence and found that 63% of the time the killer lived within a 6 mile traveling distance to the crime scene. So putting all these factors together we could expect the Zodiac Killer's first murders at Lake Herman Road on December 20th 1968 to be only a matter of a few miles from his house. Bearing in mind the timeline that night, given by eyewitnesses Stella Medeiros and James Owen, it was determined the Zodiac Killer after brutally murdering David Faraday and Betty Lou Jensen must have driven east after the commission of the crime and headed toward Benicia. Using this as our guide, there may be a good chance that if you were to travel by vehicle from the Lake Herman Road turnout toward Benicia in your car, you may be near or have already passed the home of the Zodiac Killer, within or close to this six mile journey.
A recent survey in Germany studied the locations of serial killer victims in respect to the killer's home residence and found that 63% of the time the killer lived within a 6 mile traveling distance to the crime scene. So putting all these factors together we could expect the Zodiac Killer's first murders at Lake Herman Road on December 20th 1968 to be only a matter of a few miles from his house. Bearing in mind the timeline that night, given by eyewitnesses Stella Medeiros and James Owen, it was determined the Zodiac Killer after brutally murdering David Faraday and Betty Lou Jensen must have driven east after the commission of the crime and headed toward Benicia. Using this as our guide, there may be a good chance that if you were to travel by vehicle from the Lake Herman Road turnout toward Benicia in your car, you may be near or have already passed the home of the Zodiac Killer, within or close to this six mile journey.
It is a distinct possibility the Zodiac Killer had a standard Monday to Friday, 9-5 occupation, when you consider his four confirmed crimes. If he lived in Vallejo or Benicia, then the first two crimes at Lake Herman Road and Blue Rock Springs were close to his home. This makes perfect sense in respect to the 'least effort principle', as both of these attacks were on a Friday, a day he may have worked. His final two attacks at Lake Berryessa and Presidio Heights were further away, but both were perpetrated on a Saturday, a day he may not have worked. This would have given him more time and energy to plan a more distant and ultimately more daring attack.
If we take the 'least effort principle', 'buffer zone' and the time constraints of his occupation into account, it makes San Francisco an unlikely home for the Zodiac Killer, assuming he remained in one location throughout his four attacks. If we take the mileage from the nearest point in San Francisco to the Lake Herman Road turnout, it is approximately 38 miles. See here. Therefore, the geographical profiling principle would be turned on its head. The Zodiac Killer would have finished work on Friday and have been prepared to throw the 'least effort principle' out of the window and create his initial 'buffer zone' at 38 miles or more when carrying out the Lake Herman Road attack. This would be followed by a 44 miles or more 'buffer zone' at Blue Rock Springs, and then he would have traveled even further, a distance of 80 miles to Lake Berryessa for his third attack, before finishing closest to his home residence with the murder of Paul Stine on October 11th 1969. It would mean he was committing three crimes in excess of 38 miles away, in less familiar areas, such as the rarely used Lake Herman Road, with less escape routes, as his opening gambit. In addition, he was prepared to expose himself even further by traveling on foot in a built up area, having just shot a taxicab driver and securing a 'trophy', all within the nearest point to his home residence.
The first two attacks also suggested the killer must have had prior knowledge that Lake Herman Road and Blue Rock Springs Park were popular haunts for courting couples, unlikely to have been known by a native of San Francisco - unless he worked in the locality of Vallejo or Benicia, or had previously lived there.
If we take the 'least effort principle', 'buffer zone' and the time constraints of his occupation into account, it makes San Francisco an unlikely home for the Zodiac Killer, assuming he remained in one location throughout his four attacks. If we take the mileage from the nearest point in San Francisco to the Lake Herman Road turnout, it is approximately 38 miles. See here. Therefore, the geographical profiling principle would be turned on its head. The Zodiac Killer would have finished work on Friday and have been prepared to throw the 'least effort principle' out of the window and create his initial 'buffer zone' at 38 miles or more when carrying out the Lake Herman Road attack. This would be followed by a 44 miles or more 'buffer zone' at Blue Rock Springs, and then he would have traveled even further, a distance of 80 miles to Lake Berryessa for his third attack, before finishing closest to his home residence with the murder of Paul Stine on October 11th 1969. It would mean he was committing three crimes in excess of 38 miles away, in less familiar areas, such as the rarely used Lake Herman Road, with less escape routes, as his opening gambit. In addition, he was prepared to expose himself even further by traveling on foot in a built up area, having just shot a taxicab driver and securing a 'trophy', all within the nearest point to his home residence.
The first two attacks also suggested the killer must have had prior knowledge that Lake Herman Road and Blue Rock Springs Park were popular haunts for courting couples, unlikely to have been known by a native of San Francisco - unless he worked in the locality of Vallejo or Benicia, or had previously lived there.
Canter and Larkin (1993) proposed the 'circle theory of environmental range', that suggests a circle drawn around the crime scenes (four in our case) should result in the killer's home residence lying somewhere within this circle. It is then a matter of narrowing it down using the principles detailed above. The killer generally starts his crimes closer to home, yet in the case of San Francisco, this is the Zodiac Killer's final crime. It should therefore be one of the furthest from his home location. The Lake Herman Road and Blue Rock Springs locations lie extremely close to the center within the circle. This is not conclusive, but it is definitely food for thought when we further consider the immediate movements of our killer from Lake Berryessa to the payphone at 1231 Main Street in downtown Napa. The murderer would be traveling in a southerly direction, that would be on a collision course with the Vallejo/Benicia areas.
Furthermore, the unexplained 40 minutes after the Blue Rock Springs attack raises questions, considering the payphone was only 10 minutes journey time from the crime scene. If the killer had lived in San Francisco, he could have made this phone call anywhere en route with little risk. There would have been no reason for him to hang around Vallejo, spending 30 minutes longer than necessary to place the call to Nancy Slover, with all the risks this would have entailed.
Another geographical profiling term is 'distance decay', that states the farther you travel away from the killer's comfort zone (their area of familiarity), the less likely they are to kill. Although we only have four crime scenes on our map above, it nevertheless would exhibit this trait, based on a premise of our killer living close to both Lake Herman Road and Blue Rock Springs Park. The cluster of pins in the map would therefore decay the further we traveled from the murderer's base location. It is hard to call the first two crimes a cluster, but so far they are more suggestive of a warm zone than San Francisco regarding the circumference of our circle. It is true that many Zodiac letters were mailed from San Francisco, but this is more than likely where he worked, as opposed to where he lived, and he mailed these letters on his journey to and from work. Had he finished work at 5:00 pm on Friday afternoon in San Francisco and arrived back in Benicia or Vallejo sometime approaching 6:00 pm, the 'least effort principle' would now kick in. This was ultimately reflected in his choice of locations on December 20th 1968 and July 4th 1969. In fact, the further away his workplace was, the greater this 'least effort principle' would apply, not only because of tiredness, but the time constraints of traveling further afield. In all probability the Zodiac Killer lived in either Vallejo or Benicia - which leaves one final question.
Bearing in mind the double murder at Lake Herman Road on December 20th 1968 at the dead of night, with the killer having fired off at least ten rounds, probably having picked up biological transference from the brutal execution of David Faraday, carrying the smoking gun, having limited escape routes, and in all likelihood, heading for the safety of home, did he turn left to Vallejo, or right to Benicia. This may be the answer we are looking for.
See also:
http://www.zodiacciphers.com/zodiac-news/the-first-phone-call
http://www.zodiacciphers.com/zodiac-news/springs-and-tuolumne
http://www.zodiacciphers.com/zodiac-news/four-minutes-behind
Furthermore, the unexplained 40 minutes after the Blue Rock Springs attack raises questions, considering the payphone was only 10 minutes journey time from the crime scene. If the killer had lived in San Francisco, he could have made this phone call anywhere en route with little risk. There would have been no reason for him to hang around Vallejo, spending 30 minutes longer than necessary to place the call to Nancy Slover, with all the risks this would have entailed.
Another geographical profiling term is 'distance decay', that states the farther you travel away from the killer's comfort zone (their area of familiarity), the less likely they are to kill. Although we only have four crime scenes on our map above, it nevertheless would exhibit this trait, based on a premise of our killer living close to both Lake Herman Road and Blue Rock Springs Park. The cluster of pins in the map would therefore decay the further we traveled from the murderer's base location. It is hard to call the first two crimes a cluster, but so far they are more suggestive of a warm zone than San Francisco regarding the circumference of our circle. It is true that many Zodiac letters were mailed from San Francisco, but this is more than likely where he worked, as opposed to where he lived, and he mailed these letters on his journey to and from work. Had he finished work at 5:00 pm on Friday afternoon in San Francisco and arrived back in Benicia or Vallejo sometime approaching 6:00 pm, the 'least effort principle' would now kick in. This was ultimately reflected in his choice of locations on December 20th 1968 and July 4th 1969. In fact, the further away his workplace was, the greater this 'least effort principle' would apply, not only because of tiredness, but the time constraints of traveling further afield. In all probability the Zodiac Killer lived in either Vallejo or Benicia - which leaves one final question.
Bearing in mind the double murder at Lake Herman Road on December 20th 1968 at the dead of night, with the killer having fired off at least ten rounds, probably having picked up biological transference from the brutal execution of David Faraday, carrying the smoking gun, having limited escape routes, and in all likelihood, heading for the safety of home, did he turn left to Vallejo, or right to Benicia. This may be the answer we are looking for.
See also:
http://www.zodiacciphers.com/zodiac-news/the-first-phone-call
http://www.zodiacciphers.com/zodiac-news/springs-and-tuolumne
http://www.zodiacciphers.com/zodiac-news/four-minutes-behind
