Dr Kent Kiehl spends his days talking to people who have no compassion or empathy for others.
They are rapists and murderers. He studies their brains in an effort to understand the science of people who have no conscience.
He has the world's largest database of brain data on psychopaths. And they don't come to him - he goes to them.
Dr Kiehl has an MRI machine parked on the grounds of a correctional facility in New Mexico in southwestern United States to help his research for the Mind Research Network and the University of New Mexico.
His book, The Psychopath Whisperer is full of encounters with the psychopaths he has been interviewing for more than 20 years. So far he has scanned the brains of about 3000 violent offenders, 500 of them psychopaths.
So what made him want to know more about the brains of some of our most dangerous people?
When Dr Kiehl was 8, his father Jeff, a copy editor at the Tacoma News Tribune, came home talking about a local man called Ted Bundy.
"This was a guy who had grown up just down the street, and he had supposedly killed all these women," Dr Kiehl says.
Bundy, whose family moved to Tacoma when he was a child, is known to have sexually assaulted and murdered at least thirty women in the 1970s.
Later while studying psychology at the University of California his academic mentor there steered him in the direction of combining his interest in the brain and how someone could behave as Bundy did.
Psychopaths suffer from severe emotional detachment. They lack both empathy and remorse. Dr Kiehl has found that they make up about 16 percent of the U.S. prison population. Such people also comprise about 1 percent of the general population.
So what fascinates us about psychopaths?
"I think it's the same fascination that got me started; which is they're just so different from the rest of us, and they do things that are just inexplicable," Dr Kiehl says.