There was a Horizon program on this a short time ago.
There is a genetic facture in most psychopaths - that in itself it seems is not sufficient to make you a psychopath - infact one of the researchers had the gene.
However if you have the gene and have an abused or particularly troubled childhood that seems to do it.
The main researcher gave evidence at a trial in the US with the aim of showing diminished (note diminished not absent) responsibility. The aim was to reduce the likely sentence from the death penalty.
He was somewhat surprised that the jury then found the defendant not guilty of murder but of manslaughter (I may have the specific US legal terms wrong).
I believe that the question of how much weight such factors deserve is still fairly contraversial.
http://www.guardian.c...iew-horizon-good-evil
It occurs to me that such genetic factors could work against someone too!
If you have this genetic tendency to such an extent that it reduces your responsibility- why would you ever qualify for parole?