Louis Theroux does not always seem sincere in what he does; he plays the innocent abroad very well – even when he is basically feeding a ropes to his subjects to let them go the hanging themselves. In this documentary he does play his neutral self, but he does so to good effect rather than to trick or trap. In doing this the 2-part documentary treats its subjects with respect – even when what they say has scope for mockery or comedy (such as the reason for someone driving recklessly).In doing this he lets the subject speak for itself, and it is a chilling subject. The wider question of what is to be done, what defines insanity, and the treatment of those involved, all sit behind an array of characters who range from the eccentric to the chilling. The documentary gives them time and is not shy about what crimes they had committed; it is a tough watch in many ways as one thinks of the lives affected – both perpetrator and victims. Theroux explores the subject really well; he doesn't push anyone even when he is asking them tough questions – he does have a knack for getting people to open up as he does here.It is a little unsatisfying in the way in which doesn't provide a great sense of closure – but then to be fair, the point is that there are no easy answers to any of it.