Here's a surprising look at the average serial killer

When people think "serial killer," a face like Ted Bundy comes to mind - a relatively young, white male who's charming and intelligent.

But according to the Serial Killer Information Center, started by Dr. Mike Aamodt, a professor of psychology at Radford University, that isn't entirely true.

His database has identified over 2,600 serial killers, which Aamodt defined as somebody who killed at least two people, in two separate instances, with a "cooling off" period in between. Mass killers, however, typically kill a large number of people (usually four or more) in a single incident. Aamodt's definition differs slightly from the FBI's, which doesn't require a cooling off between killings.

Surprisingly, only 12.5% of US serial killers in Aamodt's database fit what most consider the typical profile - a white male in his late mid- to late-20s. While 92.3% of US serial killers (94.4% internationally) are male, only 52.1% are white. Only 27% are in their mid- to late-20s.

From 1990 to 2010, the most recent year of data in the project, 52.1% of US serials killers were white, while 40.3% were black. The numbers don't change much internationally either. Worldwide, 56.2% are white, while 30% are black.

"Note that when discussing the race or sex percentages, it is important to look at trends across time," Aamodt told Business Insider via email. "For example, if you combine US serial killers across all decades, 52% of serial killers have been white [and] 40% black .... However, if you just look at the past three decades: 37% were white [and] 60% were black. A very different picture!"*

Serial killers don't always act alone either. Three basic types exist: individual, team (two or more), and organizational, which can include gangs, criminal enterprises, and even terrorist groups.

Even excluding these "organizational" serial killers, Aamodt found that 36.2% are white, while 55.1% are black.

Some other interesting statistics that Aamodt determined:

• The average serial killer has an IQ 94.7. Although various tests measure IQ, 90 to 110 is usually considered "average" intelligence. A serial killer with average IQ is also the most likely to strangle or shoot their victims. Serial killers who have used bombs show, on average, higher IQs, while those who used poison exhibited the lowest.
• For male serial killers, the average age they first killed at is 27.5, while for females it's a bit older at 31.
  
• Overwhelmingly, serial killers haven't served in the military - only 23.9% did. The Army is the branch most likely to include serial killers, while the Coast Guard is the least likely.
• 85.6% come from homes with at least one biological parent, though their family life was likely unstable. While 70% reported no abuse as children, many wet the bed, tortured animals, and started fires.
• 40.5% kill for enjoyment, such as lust, thrill, or power, according to Aamodt.

The database has identified 2,624 serial killers in the US, while other countries only claim 1,249. That could lead someone to believethat the US has more serial killers than the rest of the world combined, but that's not necessarily correct.

"It would be more accurate to say that more serial killers have been identified in the US than in the rest of the world combined," Aamodt said. "The murder rate for the US falls about in the middle of the rate for other countries. Thus, it doesn't make sense that the US murder rate is average yet its serial killer rate is by far the top."

Aamodt gathered the information in his database using true-crime books, newspaper articles, prison records, court documents, and other historical sources of information. He started the Serial Killer Information Center in 1992 to provide his students, as well as the media, with accurate information regarding serial killers.

Aamodt, however, isn't the only one trying to find more accurate information about serial killers. Criminologist Eric Hickey has done considerable research on what constitutes a serial killing and how to identify those responsible, especially women. Contrary to Aamodt's research, about one in six serial killers are women, The New Yorker reported. These women, as "quiet killers" who often target family, simply aren't as easy to detect, Hickey explained to the publication.

The definition of a serial killer can also vary, just as the FBI's does from Aadmodt's. Penn State psychology professor Marissa Harrison served as the lead author on a March 2015 study revolving around female serial killers. She, for example, defines a serial killer as someone who kills three or more people, with a "cooling off" period, the Washington Post reported.

She also reiterated Hickey's point about detection. Female serial killers evade arrest almost twice as long as their male counterparts, Harrison told the Post.

Other organizations, such as the National Center for the Analysis of Violent Crime, established to aid the FBI in investigations, also conduct research regarding serial killers. A recent study from 2014 focused on details about the victims - and how that contributes to the typical portrait of a serial killer.

*Percentages were rounded to the nearest decimal.