Is there a natural born killer? Do bad brains cause bad behavior? And if so, what are we going to do about it? With increasing frequency, research suggests there is no single, simple answer to questions regarding criminal behaviour. Studies of murderers, psychopaths, and aggressive children are increasingly implicating birth complications, structural and functional brain deficits, genetic abnormalities, and poor nutrition as causes of crime. It is argued that the future key to curing crime lies in a more complex integration of biological and social knowledge, but this in turn raises important ethical and legal questions regarding our concepts of free will, moral responsibility, and punishment.