The most prolific American serial killer, Gary Ridgway, had a reported IQ of just 82. That's well below average.

Are serial killers smart? One would think so, based on how they are depicted in books, movies and television shows — often as diabolical geniuses.

Hannibal Lecter, in the “Silence of the Lambs” film and subsequent sequels, was a brilliant, cultured and accomplished former psychiatrist and surgeon who had refined taste in art and cuisine which he spoke eloquently about.

That’s often not the reality.

Some serial killers certainly were above average in intelligence. Edmund Kemper, who murdered 10 people, including his own grandparents and mother, reportedly had an IQ of 145. But, he was the exception and not the rule. The average IQ of serial killers is 94.5 and the median is 86 based on 4,743 serial killers, according to the Serial Killer Information Center, a database created by two universities with the aim of collecting and regularly updating serial killer data. They last updated their site in 2016. Average intelligence is considered to be between 90-110 IQ. So, this study suggests that serial killers as a whole are actually on the lower side of average.

Jack Rosewood, author of “The Big Book of Serial Killers: 150 Serial Killer Files of the World's Worst Murderers,” told Oxygen.com that the misconception that serial killers are all geniuses may stem from the fact that the few serial killers who are highly intelligent — like Jeffrey Dahmer, Ted Bundy and Rodney Alcala — are more fascinating to the general public. They are therefore more studied and talked about.

“That and the fact that movies and TV rarely make a good storyline about dumb serial killers while smart killers like Hannibal Lecter and Dexter Morgan [from Showtime’s “Dexter”] makes for excellent entertainment which of course is how these stereotypes are shaped,” he said.

The smarter serial killers probably could have done more with their life if they channeled their intelligence for good. But, they were often unmotivated. Bundy reportedly had an IQ of 136 but repeatedly dropped out of colleges and worked multiple minimum-wage jobs. He was described as having a lack of ambition.

Then there’s Dahmer, who reportedly had an even higher IQ of 144. He was so charismatic as a teen that he managed to get clearance for him and two classmates to visit the White House while on a high school field trip to Washington D.C. according to the graphic novel “My Friend Dahmer,” written by Dahmer’s former classmate Derf Backderf. Despite his intelligence and confidence, Dahmer didn’t succeed professionally. He was discharged from the army due to a drinking problem. Later, he was fired from his night shift job at a chocolate factory.

“A lot of high people with high IQ in society seem to have a problem with motivation,” Rosewood explained. “Dahmer and Bundy might not have been successful in the eyes of society but they were certainly above average in what motivated them - killing.”

Authorities believe that Dahmer killed 17 men and boys and Bundy killed 36 (although police believe he may have killed around 100) young women. But, the American serial killer with the most confirmed kills and who evaded police for decades was someone with a reportedly IQ of just 82, which is considered on the low side: Gary Ridgway.

gary ridgway getty

Ridgway (pictured above), known as the “Green River Killer” was convicted of killing 49 people, yet he confessed to killing 71. He began killing in 1982 but wasn’t caught by police until 2001.

“So while he certainly isn't the most intelligent man, he somehow has the most confirmed kills in the United States,” Rosewood said.

Randy Woodfield, the I-5 Killer, had an IQ of about 100, according to Ann Rule’s book “The I-5 Killer.” That’s about average. Like Ridgway though, the authorities believe he was a prolific killer. Though he was only convicted for one murder he has been linked to 18 and police believe it is possible he killed a total of 44 throughout Washington state, Oregon, and California within a time span of just one year, between 1980 and 1981.

Dennis Rader, also known as the “BTK (Bind, Torture, Kill) Killer,” taunted the media for decades and got away with it. He killed 10 people between 1974 and 1991. But was he smart? He was eventually caught in 2005 after he actually asked the police in a letter if a floppy disk could be traced back to him or not. The police answered his question in a newspaper ad saying that it could not. They lied. Soon enough Rader followed their advice and sent a floppy disk to a local television station, which led to his capture. Not the most clever move.

“He was patient with his murders which is probably why he got away with it for so long,” Rosewood explained, adding that he didn’t find Rader to be very smart. It’s unclear what Rader’s IQ is. “At the end of the day he got caught because he liked to taunt the media and the police.”

Peter Vronksy has PhD in criminal justice history and is the author of three books about serial killers: "Serial Killers: The Method and Madness of Monsters," "Female Serial Killers" and "Sons of Cain: A History of Serial Killers From the Stone Age to the Present." He told Oxgyen.com that America's deadliest serial killer to date, Ridgway, was long suspected of being the "Green River Killer," who targeted sex workers. So, he wasn't exactly invisible, just hard to arrest.

“When you target street prostitutes, you’re targeting victims that often have unstable families," Vronsky explained. "Nobody knows when they were seen for the last time. Often they are working independently. [...] So, it’s very difficult to build a timetable of where maybe the victim and the suspect intersected."

Ridgway was also questioned several times by investigators but police lacked the evidence to catch him until 2001, when DNA linked him to the crimes. So perhaps it wasn't because of being clever that he evaded the police but rather because of older forensic technology and profiling. Vronsky said back in the 1970s and '80s, police suffered from “linkage blindness.” The term "serial killer” was only coined in the 1980s.

"With Bundy, police could not imagine a single perpetrator committing so many murders in so many jurisdictions," Vronsky said. "On top of that, jurisdictions didn’t talk to each other either. Today is a different era."

Now, we have technological databases, major advances in DNA technology and cell phone data and most departments are familiar with what a serial killer does.

"We are starting to see arrests today where budding and wannabe serial killers are caught," Vronsky said. “We are apprehending them after their first murder. They never get a chance to become a serial killer.”

It's a lot harder to get away with murder these days and more difficult for serial killers to outsmart the system. That doesn't mean their urge to kill is going anywhere. What serial killers lack in superior intelligence, they make up for in predatory instincts.

Vronsky told Oxygen.com that “what serial killers have is a highly developed sense of animal cunning which we commonly mistake for intelligence. They’re hunters. They also have an instinct for manipulation and finding people’s weaknesses. They can smell that out. Often we mistake those instincts, those destructive animalistic predatory instincts for intelligence.”

So, the Hannibal Lecter and Dexter Morgan types are pretty much myths.

“You don’t have the Hannibal Lecter kind of elegant super-intelligent serial killers."

[Photos: Getty Images]