My Science Fiction novel trilogy, Descent, features two rather evil characters (among others) as chief protagonists; one is a nascent psychopath. As the novel is written entirely from a first-person perspective, this is a problem; what goes on in the mind of a psychopath? How do I write a psychopathic character?
Movies (think Silence of the Lambs, etc.) have an advantage over novels in this regard. Everything happens on screen, it is all action and motion, and very rarely any 'internalized thoughts' or overlay. So the psychopath on screen is what she or he is, and that's easily understood.
However, if you want to get into their heads with the written word, it is tricky. Non-psychopaths tend to have active thought lives, a bit of to and fro in their minds, argument, observation, the inner self-talk we all have (and at times hate). This leads to wonderful (from the writing perspective) self-doubt, confusion, guilt, emotion and conflict.
For the psychopath, this is not the case. Their inner thought life is, as Dr. Robert Hare puts it, "banal, sophomoric, and devoid of the detail that enriches the lives of normal adults". There's none of the inner turmoil that makes a character engaging or interesting. They end up as two-dimensional characters, lacking emotional depth and nuance because, quite simply, that is what they are.
Tackling a psychopath in the third person is (I think) a better solution; show them in action, use the other characters for internal conflict, then you have something. And I think (barring Atticus Lish) this is the way most authors approach it.
Me, well, I have to be different, don't I? (or as my high school English teacher said, 'A royal pain in the arse'). So for me, writing in first-person, my character ends up as "nascent psychopath lites"; a long way towards a true psychopath but falling short enough to make his inner self interesting.
Check out the blurb for the first installment of Descent here. And if you haven't read my first novel, Sha'Kert: End of Night, click the link below to get it on ebook: