How Many Serial Killers are in the United States? One Scientist Believes It Could Be Thousands

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A new report from The New Yorker estimates that 2,000 serial killers are currently at large in the United States. According to archivist and researcher Thomas Hargrove, tracking the habits and status of serial killers comes down to data analysis, which he's been carrying out independently for years.

Hargrove is a part of the Murder Accountability Project (MAP), a non-profit that aggregates data on homicides and feeds it into Hargrove's algorithm, which he sometimes refers to as a serial killer detector. Serial murder, according to the FBI's official definition, is the "unlawful killing of two or more victims by the same offender(s), in separate events." A pause in between murders is sometimes referred to as a "cooling off period".

In 2016, Vox published analysis of similar data from Dr. Mike Aamodt at Radford University in Virginia. He found that serial killers were on the decline, as a whole, and that most killed simply because they enjoyed it.

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A Vox data visualization of homicide data from Radford University outlines the typical determined motives of a serial killer. Vox

According to the Radford Serial Killer Data Base, another research project noted by The New Yorker, American serial killers are 10 times more likely to be male than female, and their average I.Q. is only 94.5. The national average I.Q. among all American citizens is 98. The database also divides serial killers into archetypes, which are as follows:

"Missionaries" believe they're on quests to rid the world of immoral people, "black widows" marry and kill multiple husbands, "bluebeards" are men who kill exclusively women, either for money or to be feel powerful. "Angels of death" are professional female caretakers or nurses who kill their patients, "trollers" meet their victims by chance, and "trappers" monitor their victims ahead of time or situate themselves in professions where potential victims come to them.

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Hargrove in an appearance on ABC News. ABC

As for Hargrove's estimate that 2,000 serial killers are still at large in the United States, he says it's the number he came to after analyzing data available. Hargrove told The New Yorker that according to the FBI, 1,400 murders remain unsolved but are linked to other killings through DNA. That's only slightly above 2% of murders investigated by the FBI.

"Those are just the cases they were able to lock down with DNA," Hargrove said. "And killers don't always leave DNA—it's a gift when you get it. So two per cent is a floor, not a ceiling."

Anyone proficient in coding can use Hargrove's algorithm on the MAP website. But if a user wants to know how many unsolved murder cases are still open in their region, they can simply use the website's search function.