What Are These?

The Murder Accountability Project has developed an algorithm capable of detecting serial killers who target multiple victims using similar methods of killing within a specific geographic area. This technique can be useful to police in detecting difficult-to-see patterns over a period of several years or longer.

The algorithm is based upon a reasonable premise -- an active serial killer can reduce the normal (or expected) clearance rate for groups of similar victims killed through similar methods. The algorithm organizes more than 700,000 homicides into about 100,000 clusters by generating a unique Murder Group number based upon the geography (either county or metropolitan area), victims' gender and method of killing.

The algorithm looks for clusters with very low solution rates.

By moving the "% Solved" slider, you can adjust the sensitivity of the search. Higher settings will produce more suspicious clusters, but also increase the odds that other factors influenced the failure rate of police investigations. By concentrating on a particular city, careful manipulation of the "solved" selector demonstrate what kind of homicides are the most difficult to solve.

To see the victims of "Green River Killer" Gary Ridgway, set the cluster maps to the years 1980 to 2000, and the "% Solved" selector to an unusually low rate of homicide clearance, perhaps 25 percent or 33 percent. You will see a large circle above the Seattle area. These are women who were killed by "other or type unknown" weapons. Since most of Ridgway's 48 female victims were found out-of-doors, medical examiners usually had difficulty determining the precise cause of death.

The Murder Accountability Project believes these clusters with lower-than-expected clearance rates have an elevated probability of containing serial killings. But they are not proof of the presence or absence of multiple-victim offenders.

Rarely are all of the victims within a cluster the handiwork of serial killers. Police investigation – including physical evidence, offender confession, or witness testimony – is the best evidence that a cluster of homicides may be linked.

To see the algorithm written in SPSS syntax (which can be translated into other statistical software systems) click here.  These visualizations were developed by Haneesh Marella and donated to the Murder Accountability Project. Contact Haneesh through his LinkedIn account here.

DISCLAIMER: The Murder Accountability Project (MAP) and its Board of Directors make no warranty, expressed or implied, to readers and users of the MAP website (www.murderdata.org) and accept no responsibility for its use, nor for any harm, loss or damage resulting from reliance on any tools, data, information or other content made available through the MAP website. The MAP website is provided for informational and non-commercial purposes only. The readers assume sole responsibility for determining the appropriateness of its suggested use in any particular methodology, calculation, or serial homicide model; for any conclusions drawn from the results of its use; and for any actions taken or not taken as a result of analyses performed using MAP’s online tools.

MAP’s homicide detection methodologies are based on datasets maintained by the Federal Bureau of Investigation or case data MAP obtained directly from police agencies that do not report data to the FBI. MAP does not guarantee the accuracy, completeness, reliability, availability, or usefulness of these datasets. MAP’s serial homicide detection methodologies may or may not have predictive value when applied to specific circumstances and to specific cases. These methods in the past have detected both known and previously unknown serial homicides. But users are warned that these methods also can produce false results, either by making false matches between unrelated cases or by failing to detect known linked cases. The rate of failure is currently unknown. The ultimate authority on whether homicide cases should be linked rests with the law enforcement agencies which investigate crimes and with the appropriate courts of criminal law.

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