Looking at the most-streamed movies or television shows on any given streaming service, it would be easy to assume that serial killers lurk behind every corner. The stories of Jeffrey Dahmer, Ted Bundy and the Boston Strangler still loom large––even if the likelihood that you’ll encounter another Zodiac Killer has never been lower.

Since the 1970s and 1980s, a high activity period for serial murderers, the numbers have dropped significantly. Numbers peaked in the 1970s when there were nearly 300 known active serial killers in the U.S. In the 1980s, there were more than 250 active killers who accounted for between 120 and 180 deaths per year. By the time the 2010s rolled around there were fewer than 50 known active killers. 

This data is based on numbers from the Radford University/Florida Gulf Coast University Serial Killer Database that have been further analyzed, combed through and published in the recently-updated “Extreme Killing: Understanding Serial and Mass Murder” by James Alan Fox, Jack Levin, Emma Fridel.

But what accounts for this dramatic decrease over the last 40 years?

According to Fox, a criminology professor at Northeastern University, it comes down to several major changes in forensic science, policing, criminal justice and technology that have made it harder than ever for the BTK Killers of the world to escape capture.

The decline that started in the 1980s mirrors a decrease in a nationwide crackdown on crime that occurred in the 1980s and 1990s made it difficult for serial killers, let alone anyone involved in violent crime, to stay out of prison.

“Part of it has to do with the same reason the murder rate has gone down,” Fox says. “You have a surging number of people behind bars, so some of the would-be serial killers were likely behind bars as opposed to in the bars looking for victims.”

Between 1980 and 1992, the incarceration rate in federal and state prisons more than doubled to 332 per 100,000 U.S. residents, according to the Bureau of Justice Statistics.

Advances in forensic science and DNA testing have also made it possible for police to more effectively investigate murders, even those that have remained open or questionable for decades. 

“The first case I was involved with in 1990, I was on a task force investigating the murders of five college students,” Fox says. “We had DNA, but it was pretty crude. We couldn’t get DNA from hair––now you can. You needed a lot of genetic material to be able to identify the DNA pattern––now you don’t.”

Forensic genealogy, recently used in the case of suspected quadruple murderer Bryan Kohlberger, has even made it possible to test DNA collected at a crime scene against DNA collected from a suspect’s family. 

And serial killers can leave a digital fingerprint too. Fox says the proliferation of surveillance cameras and the advent of the cellphone with its GPS tracking capabilities have made it harder for serial killers to abduct their victims in the first place. Investigators also have even more tools at their disposal to track a killer’s whereabouts, whether it’s an IP address or, in the case of the BTK Killer, the metadata off of a floppy disk.

Fox also attributes the decrease in serial killers to changing behaviors among the public as well. With widespread social and cultural changes in the 60s and 70s––drug use, hitchhiking, the hippie movement, anti-establishment sentiment––conditions were prime for predators to go on the prowl, Fox says.

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But things have changed in the last few decades. Fears around mass killings have increased, as has the public’s general anxiety and distrust for one another. People are “much more aware and cautious than we used to be” and might be less likely to accept help from a stranger who says they just want to help you fix your flat tire.

Changes in how parents think about their children’s safety also mean some of the most common targets for serial killers, young women and girls, are less vulnerable than in decades past. According to Fox, Levin and Fridel, of the 5,582 victims killed by serial killers since 1970, more than half are female. About 30.2% of those female victims are between the ages of 20 and 29 and 23% are between the ages of 5 and 19.

Laurie Kramer, a professor of applied psychology at Northeastern, says many parents now feel like the world is a “more dangerous and risky” place, even at school, places they previously assumed were “risk free.”

“There is that sense that parents need to be much more participatory and intentional about selecting those opportunities in which their kids are going to be beyond school and church or other sorts of things that are pretty normative for them,” Kramer says. “There’s just a general anxiety, and I think that plays out with being protective.”

Kramer also speculates that the shift toward social emotional learning that occurred in school systems across the country over the last decade could partly explain why there are fewer serial killers now. SEL helps students develop empathy and manage their frustration and anger, while also giving educators a chance to “compensate for some trauma that kids may have experienced in other settings, like their homes,” Kramer says. Although it’s not a guaranteed fix, that extra layer of support could help prevent potential serial killers from developing in the first place.

“By having some ability to identify individuals early in life who are having difficulty, to provide appropriate forms of intervention and treatment earlier and to provide more effective forms of treatment, all of this is improving,” Kramer says.

Even though there are fewer serial killers stalking American streets, the culture at large remains fascinated by the horrific, sordid tales of who Fox calls “the legacy killers.” Serial killers may have an oversized cultural presence given how unlikely it is for people to encounter them, but Fox says it is still vitally important to study and, hopefully, prevent them from killing.

“The Boston Strangler killed 13 people and impacted their loved ones, but also was able to hold this entire city in a grip of terror for years,” Fox says. “The idea that there was one person who wreaked so much havoc on the city, whatever we can do to understand and prevent and capture someone like that early on, the better off we are.”

Cody Mello-Klein is a Northeastern Global News reporter. Email him at c.mello-klein@northeastern.edu. Follow him on X/Twitter @Proelectioneer.