True Crime Expert Reveals His Pick For The Most Terrifying Serial Killer - Exclusive

Depending on who you ask, some of the most infamous serial killers of all time include John Wayne Gacy and Ted Bundy (via Britannica). Others might say no ranking of the most notorious serial killers is complete without Ed Gein, Jack the Ripper, or H.H. Holmes (per History). But truly, the list of infamous serial killers only goes on from there. All are guilty of horrific and tragic crimes that no one should aspire to. From a psychological perspective, though, they are all really fascinating to learn and read about.

Really, though, how does someone rank the kind of heinous acts that serial killers are capable of? According to NPR, speaking with forensic psychologist and Columbia University professor Michael Stone in 2010, a three-tier system can be used: Those who impulsively commit an isolated act of evil, the only mildly psychotic, and finally, the extremely psychotic. Who, then, is the most terrifying serial killer of all? We checked in with Mike Oh, creator of the true-crime YouTube channel "That Chapter." Here's what he had to say.

The most terrifying serial killer was only officially linked to three murders

Speaking exclusively with Grunge, Oh says in his expert opinion, Israel Keyes is the most terrifying serial killer of them all. Arrested in 2012 in connection to a young woman's disappearance in Alaska, Keyes was only officially linked to three murders. Once in custody, though, Keyes confessed to many more, according to CBS News. Born in 1978, Keyes died by suicide behind bars shortly after his arrest in 2012, and it's believed that he killed a total of 11 people in his lifetime, if not more, as Biography notes. In his childhood, Keyes had a fascination with fire and was also known to torture animals — known hallmarks of serial killers.

According to Oh, "He's almost like a serial killer's serial killer. He escalated from sexual assault to murders, the extent of which we don't know but is probably fairly sizable." And though Keyes was only definitively linked to three murders, "each of which was horrific in its own right," Oh says, his extensive travel across the U.S. leads law enforcement to believe he had a hand in a number of cold cases across the nation. Oh explains, "When a serial killer has 'kill kits' buried in various locations, he would have been eager to get his money's worth."

If you or anyone you know is having suicidal thoughts, please call the National Suicide Prevention Lifeline​ at​ 1-800-273-TALK (8255)​.

Keyes was a fan of serial killers

According to Oh, another chilling detail about Israel Keyes is how carefully he studied the methods and patterns of infamous serial killers who came before him. "He studied well and knew what he was doing," Oh says. Under intensive interrogation, Keyes died by suicide while in custody with a razor blade that was somehow illicitly smuggled into his jail cell. He also attempted to strangle himself using bed sheets, as CBS News goes on to report.

As Oh explains, Keyes would target his victims at random, and when Keyes was finally caught, "... he happily confessed to one murder, laughed throughout most of the interviews, and then killed himself, painting Satanic symbols with his own blood on the walls," Oh says. "Really ticks all the boxes you don't want someone to tick, and he probably ticked many more we will never know."

To get some sense of how clearly depraved Keyes was, Oh says, "Just listen to the sound of and how often he laughs in his police interviews," many of which are available to watch now on YouTube. According to Oh, the most terrifying serial killer of them all "... could probably kill a few people with that alone."