the brain is complex but new technology is being used to explain psychopaths like brian dougan.s. he's scanned more criminal plains than anyone in the world. the brain function of the psychopath is abnormal. dr. keel used brian dougan's scans to demonstrate to the jury that a psychopath's brain look different. >> the area where you would show things like understanding, ever this, some decision making, he had no gray matter which means there was nothing there that was firing properly. >> reporter: the defense team's hope was not to excuse dougan of responsibility but to save him from execution. >> i think people were afraid of what we were bringing forward. because people want to think that criminals are just evil people. and if someone has a physical defect, then we should look at them differently and not necessarily put them to death. >> reporter: in 1982, john hinkly jr. shot that -- that effected the behavior when he shot and wounded president reagan. james cavanaugh was an expert for the hinkly trial and then for dougan. he says you cannot execute an individual because their