Horizon - man and science today

The detective tries to find the motive for murder. The psychiatrist looks for the cause.
Hidden somewhere beneath layers of emotion certain patterns of behaviour and personality can combine with circumstance to produce an explosive mixture resulting in violent death. In a few cases the pattern may be recognised and the killing prevented. How much does science yet understand about a man who kills, and how can that man come to terms with himself after a conviction for murder?
(Colour)