This story was originally published on June 15, 2018.

No one told James Fallon he was a psychopath.

Or maybe they had. When he was young, he'd heard again and again from people in positions of authority — a priest, a professor, a friend's father — that there was something off about him. Something dark that they couldn't quite name. But Fallon brushed it off each time.

Many years later, as a professor of psychiatry at the medical school of the University of California, Irvine, Fallon discovered his psychopathic mind for himself.

"I'm a little bit of a snake, but I'm not really a bad guy," Fallon told Out in the Open host Piya Chattopadhyay. "But you don't want to be close to me."

Fallon made the discovery by accident.

In the late 1980s, the university got a PET scanner. Accused murderers were coming into the school to get brain scans done as part of their defences.

"They'd come in tied up in manacles," Fallon said. "We'd have these SWAT teams all over the roofs of the medical school."

Over the decades that followed, the school accumulated these brain scans. And as Fallon studied them, he was noticing patterns. Certain areas that light up in normal brains were dark.

"So I said, my god, there's something here."

He gave talks on his findings.

Bizarre coincidences

Meanwhile, two other events in his life were converging.

"All this happened at the same time," he said. "It was very bizarre."

Lizzie Borden was tried and acquitted for the murders of her father and stepmother in 1892, though she remains infamous. Fallon discovered that he was distantly related to Borden.

The first coincidence came when his mother told Fallon about a historical book on his father's family.

"And there's all these nasty guys in there," he said. People who weren't so different from the murderers he'd been studying.

Thomas Cornell Jr., an early colonial settler who was convicted and hanged for killing his mother, was a direct ancestor. And Lizzie Borden, who was famously tried for the axe murders of her father and stepmother in the late 19th century, was a distant cousin.

The second coincidence came through Alzheimer's research Fallon was conducting. The team had completed brain scans of patients. But they needed a control group. So Fallon put his family members, including himself, under the machines.

And as he was flipping through the pile of his family's scans, he saw one that looked identical to the killers he'd been studying.

"I said, OK guys, really funny. Ha ha," Fallon said.

He thought the lab technicians had played a joke on him, slipping a psychopath's scan into the pile with his family. They assured him that this was no joke.

"I said, 'Whoever this person is shouldn't be walking around in society.'"

The psychopathic markers were all there. The parts of the brain that regulate conscience, emotional empathy and inhibition were turned off.

"This is probably a very dangerous person," he said. "Well, I peeled back the tape over the name, and there it was. It was my name."

He laughed it off. He still didn't believe it. He'd never been a violent guy. He was married with kids. He had plenty of friends, and a successful career.

But when he got home and told his wife about it, she said to him: "It doesn't surprise me."

He came around to the idea gradually.

"I just started asking everybody, 'What do you think of me?' I started with my wife, my sister, my brothers, my parents. On and on. All the people close to me, including psychiatrists who I'd worked with for years who really knew me well. They all said — except for my mother, who said, 'No, you're a nice boy' — everybody else said, 'Wwe've been telling you for decades, for years, that you do psychopathic things.'"

He'd been emotionally unavailable, reckless, manipulative, getting by on charm and what he calls "cognitive empathy" — the ability to understand what others are feeling, without actually feeling it himself.

Assessments by his colleagues were what really convinced him. His brain scans, genetic markers and behaviours all pointed toward borderline psychopathy. If a cold-blooded killer is formed through both nature and nurture, Fallon's nature suggested he was capable of terrible things. Perhaps a lack of childhood trauma had prevented him from acting on his violent instincts, he thought.

'What would a good guy do?'

Fallon now describes himself as a "pro-social" psychopath. He's not out to prey on people. And his psychopathic tendencies are relatively benign.

Driven by what he describes as ego, Fallon put a challenge to himself: try pretending to be a nice, normal, emotionally connected guy. He'd start with his wife.

"Every time something came up where I was interacting with her socially, I just asked myself, 'What would a good guy do?'" Whereas in the past he might have made up an excuse to, for example, ditch her uncle's funeral and head down to the beach bar, he was now going to try doing right by her, despite his nature.

When she caught on that a sudden kindness had come over him, he assured her: "Don't take it seriously. It's just an experiment." But nice is nice. She didn't seem to mind.

"Strangers are very safe around me," he said. "It's when you get close to me that it's a little more dangerous, because I'm going to get you to do something you don't want to do.

"So, I'm trying to control that. I figure if I tell everybody I have this, then I can't get away with anything anymore."

This story appears in the Out in the Open episode "Impostors".