Studies of incarcerated populations show that individuals with psychopathy have distinct structural and functional brain differences, particularly showing reduced connectivity and gray matter in areas responsible for emotion regulation and empathy. Key findings include weaker connections between the amygdala and ventromedial prefrontal cortex (vmPFC), which may explain callous behavior and impulsivity.
The result is a distinct lack of "theory of mind", the ability to see things from someone else's point of view. These physical differences are attributed to both genetic and early environment. It also includes thicker cortical layers and deeper folds in certain areas.
On a personal note: I hung out with lots of criminals. Dealers, thieves, fences, murderers. They were my friends and I knew them well. A common thread was the belief that regular people were suckers for working, the act of theft was like picking ripe fruit from a vine and other people were just too dumb to see that. We had this discussion several times (I had a job). It did not end well for any of them and they all showed this same lack of empathy and a disdain for others. The other common thread among them all was having being raised by only their mother, who they basically ran right over top of from an early age. They were often very intelligent, but they did not do well in school and dropped out early (6th grade).
They say that you can look at a kid in 5k and tell, with great accuracy, how their life will turn out. Do criminals have free will? Are they responsible for their choices? Should they be punished for behaving in the way that their brain functions? Do you have free will?