As a neuroscientist, Fallon said he always believed humans were ruled solely by their genes and not their environment in the nature versus nurture debate.
"I never took it seriously," he said. "I was the poster boy for genes causing everything. But I had to eat crow and say I was wrong."
His personal story was the subject of a TED talk that went viral on YouTube in 2007 and he even had a guest role on the television show, "Criminal Minds." Fallon was contacted by literary agents last year to write a book about his experience.
He blames abuse in the first three years of life, combined with biological features that turn off serotonin in the brain, leading to psychopathic violence.
"It's a loaded gun," he said, but not necessarily a "death sentence."
Fallon suggests that a child born with biological tendencies to be a psychopath can be pushed over the edge by early abuse and by bullies.
Northeastern University criminologist Jack Levin agrees environmental influences determine whether a psychopath will go on to be violent, but discredits Fallon's theory
The author of a book about mass murderers, "Extreme Killing," Levin said most serial killers are in their 30s and 40s.
"You can determine the biological roots of psychopathy, including the lack of empathy and remorse and manipulative disposition, but the problem is, that does not necessarily translate into violent behavior," he told ABCNews.com. "There are literally millions of psychopaths."
The American Psychological Association claims that as many as 3 percent of all Americans have antisocial personalities, according to Levin, "meaning they are crafty and shrewd and masters at presentation of self."
"They might sell you a bad used car, or might be womanizers or pathological liars or cheaters, but that doesn't mean they will kill anyone," he said. "Not unless you become an obstacle to their success -- and then you better watch out."
All serial killers seem to share a "feeling of profound powerlessness," said Levin.
One of the earliest signs can be animal cruelty. "If you see a 6-year-old who sadistically abuses a dog or cat that is the family pet in an up-close and personal way, in order to maximize the suffering of the animal, clearly that's a red flag and you have a problem on your hands."
Levin suggests that psychopathic killers have difficulty transitioning from adolescence into adulthood.
"If the triggers occurred in early childhood, they would start killing people when they were 9 or 12," he said. "There is some environmental factor beyond how they were raised."
"It's impossible to predict [who will be a killer] under the Fallon model," said Levin. "A lot of people have the symptoms, but don't get the disease. They have been brutalized under terrible circumstances, been sexually stimulated by their parents and yet grow up to be healthy, decent people."
Fallon said his bad biology didn't stop his professional success, even if has taken a personal toll. Throughout life, he said he has had a larger-than-life personality that attracts people, but puts those he loves at risk.
"I wouldn't want to marry me," he said. "I am a pain in the ass and competitive. I can be so manipulative and I am always on the make, but I am not going to kill anyone or rape anyone."