Research is being done to study the brains of psychopaths in prison using a portable functional magnetic-resonance-imaging scanner, looking for a defect , with the goal of discovering a treatment.

"Although the number of psychopaths who are not in prisons is thought to exceed the number who are—if the one-per-cent figure is correct, there are more than a million psychopaths at large in the United States alone—they are much harder to identify in the outside world. Some are “successful psychopaths,” holding down good jobs in many types of industries. It is generally only if they commit a crime and enter the criminal-justice system that they become available for research."

I've known at least two psychopaths personally, neither incarcerated. They are scary people.