Kim Rossmo With the search for the infamous Zodiac Killer through DNA looking ever more threadbare, one very much overlooked tool in locating our offender is the 'science' of geographic profiling pioneered by Canadian criminologist Kim Rossmo, who utilizes the software geo-profiling tool Rigel to analyze the likely home residence of the Zodiac Killer. Rigel uses an algorithm called criminal geographic targeting (CGT) to identify hot and cold zones on a map and give the areas that our killer may (or may not) likely reside. In the case of the Zodiac Killer, it would take into account such things as the murder sites, phone calls, commuter routes, and geographic profiling models such as buffer zone, comfort zone, least effort principle, mental map, target backcloth and distance decay function. As Kim Rossmo points out, this is an accompaniment to law enforcement to narrow the pool of suspects, but takes a back seat to powerful forensic evidence. However, with limited forensic evidence available from the Zodiac crimes, this appears our best bet to narrow down the home location of our killer before venturing outwards. Searching for suspects the length and breadth of California is a thankless task, with many researchers identifying a potential suspect and ultimately layering weak circumstantial evidence upon weak circumstantial evidence, until they become convinced the totality of the evidence should now be reclassified as powerful and irrefutable proof of their suspect's guilt. There is a tendency to fit the suspect around the evidence, rather than let the evidence be the driver.
Kim Rossmo stated: "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. In respect to the killer's home residence, he continued "There's a number of possibilities. But remember, Rancho Vallejo was possibly 26,000 people at that time, of which only 13,000 will be male, and only a certain proportion of those are of the correct age, and a certain portion of those are only going to be white. Then we start looking at the neighborhoods involved, we have a pretty small subset. Then we start combining that with some of the personal and behavioral descriptors, and then we work in the vehicle information. If this case was active today, it would not be too difficult to find this person."
There is an excellent interactive online tool that has generated geo-profiling heat maps for killers such as Jack the Ripper, Dennis Rader (BTK), Atlanta Child Murders, Golden State Killer, Night Stalker, Yorkshire Ripper, Long Island Serial Killer and more. It can be found here at geographicprofiler.com. The Kim Rossmo heat map for the Zodiac Killer is located here.
You can toggle the geoprofile using the sidebar to remove the heat map and identify the locations underneath the color. The red color is the most likely residence of the Zodiac Killer, with a graded scale to the least likely areas of purple and beyond. This is classified as a percentage search cost (link) - Suspects are ranked based on their search cost—the percentage of the map searched before reaching the suspect’s anchor point. The search is conducted from the highest point of probability to the lowest; therefore, the lower the search cost, the more viable the suspect. If the geographic profile is accurate, the offender will have a low search cost. In the case of search cost, “map” refers to only the portion of the profile containing the crime scenes. As a result, suspects can have a search cost greater than 100%, which means a space larger than the area containing the crime scenes would have to be searched before reaching their anchor point.
Kim Rossmo stated: "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. In respect to the killer's home residence, he continued "There's a number of possibilities. But remember, Rancho Vallejo was possibly 26,000 people at that time, of which only 13,000 will be male, and only a certain proportion of those are of the correct age, and a certain portion of those are only going to be white. Then we start looking at the neighborhoods involved, we have a pretty small subset. Then we start combining that with some of the personal and behavioral descriptors, and then we work in the vehicle information. If this case was active today, it would not be too difficult to find this person."
There is an excellent interactive online tool that has generated geo-profiling heat maps for killers such as Jack the Ripper, Dennis Rader (BTK), Atlanta Child Murders, Golden State Killer, Night Stalker, Yorkshire Ripper, Long Island Serial Killer and more. It can be found here at geographicprofiler.com. The Kim Rossmo heat map for the Zodiac Killer is located here.
You can toggle the geoprofile using the sidebar to remove the heat map and identify the locations underneath the color. The red color is the most likely residence of the Zodiac Killer, with a graded scale to the least likely areas of purple and beyond. This is classified as a percentage search cost (link) - Suspects are ranked based on their search cost—the percentage of the map searched before reaching the suspect’s anchor point. The search is conducted from the highest point of probability to the lowest; therefore, the lower the search cost, the more viable the suspect. If the geographic profile is accurate, the offender will have a low search cost. In the case of search cost, “map” refers to only the portion of the profile containing the crime scenes. As a result, suspects can have a search cost greater than 100%, which means a space larger than the area containing the crime scenes would have to be searched before reaching their anchor point.
Zodiac Killer (hot zones). Click to view the complete geo-profile on geographicprofiler.com
One can see that the search cost is lowest for the area just east of the Napa Junction, the area of Ridgeview Park, Mare Island Naval Shipyard and across the Carquinez Strait Bridge to the area of Crockett Hills (just east of Rodeo). The area I favor, around the Springs and Tuolumne payphone, is afforded a 4% search cost. Despite the majority of the Zodiac mailings originating from San Francisco, this area features low on the geo-profiling heat map, and backed up by the statements of Kim Rossmo above. He states that "geographic profiling can't solve a crime; there are only three ways to do that - eyewitness, confession or physical evidence - the role of geographical profiling is to allow a detective to get to that stage, where he or she can apply one of those techniques sooner, faster, more effectively and more efficiently".
This means we target the red hot zones first, before extending outwards to orange, yellow, green, blue etc.The hot zones will inevitably sometimes fall over an unpopulated area, so the areas around them become the focus of our search. The technique of geographic profiling is a supportive tool to narrow the suspect pool and search parameters, especially in a case over 50 years old with limited physical evidence - narrowing the search field in order to prioritize our efforts. The possible candidates for the Zodiac Killer can be massively whittled down, as shown in the case of Rancho Vallejo, highlighted by Kim Rossmo above. After all, he did state "If this case was active today, it would not be too difficult to find this person."
This means we target the red hot zones first, before extending outwards to orange, yellow, green, blue etc.The hot zones will inevitably sometimes fall over an unpopulated area, so the areas around them become the focus of our search. The technique of geographic profiling is a supportive tool to narrow the suspect pool and search parameters, especially in a case over 50 years old with limited physical evidence - narrowing the search field in order to prioritize our efforts. The possible candidates for the Zodiac Killer can be massively whittled down, as shown in the case of Rancho Vallejo, highlighted by Kim Rossmo above. After all, he did state "If this case was active today, it would not be too difficult to find this person."
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