Isn't this a form of physical Tourette's
There's the part of the brain that filters our words and allows us to repress certain ones - when it is damaged you can get people who cannot help but shout obscenities.
Is it that much of a leap to expect there is a part of the brain that supresses similar thoughts and even actions
Damage to the Brain in such cases could make you an "evil" psychopath.
http://www.sciencedai...9/08/090804090946.htm
Of course suggesting that Iam Brady or Fred west acted because of Brain malfunction will doubtlessly be unpopular because people need to feel that evil exists and must be punished.