I remember what it was like when I was his age: when I walked along a roof ridge line or played chicken with an intercity train just to be able to feel. You’ll do anything to end the torment and break through the numbness. It’s why my heart aches for him, despite what he’s just done. When I look into his eyes, what I see is triumph – and despair. Our daughter’s physical injuries will heal. Peter’s psychic wounds are incurable.

I can’t bear to think how lonely my son must be. In violent psychopaths, there’s a strong relationship between the intensity of loneliness they experience, and the degree of violence and recklessness in their actions. Peter has few friends, despite his outward charm and affability. He spends far too much time in his own head, which is why he gets bullied at school.

I remember watching the CCTV of the two shooters at Columbine High School strolling the corridors with no semblance of fear or remorse for the appalling atrocities they were committing. And in addition to my shock and repulsion, I experienced one other very acute sensation: recognition.

I understood those boys. Worse, I could identify with them.

Not with what they did – dear God, no, not with that, never that. The pain and suffering they inflicted on the children they murdered, on those who loved them – unimaginable. But I think I understand why those two boys did what they did. Their loneliness and alienation must have been truly agonising for them to do something so inhuman.

Peter already thinks the world is against him. If I can’t turn things around for him now, eventually he’ll reach the point of no return. He’ll cut through the last thin connection to the normal world.

Shoot up a school. Abduct and smother a child.

And there’ll be nothing I can do to stop him.

SETtalks | psychologies series

Science ♦ Entertainment ♦ Technology

Inside the mind of a psychopath | Original Air Date 9 July

The transcript below has been lightly edited for length and clarity.

For most people, the ninety-nine out of a hundred who aren’t psychopaths, murder is unquestionably wrong.

You don’t even have to think about it.

It’s the ultimate crime, right? Taking a life.

We could get into the weeds debating whether child abuse or betraying your country are actually worse than murder, but generally speaking I think most people can agree stabbing an old lady to death for her handbag is one of the most heinous crimes there is.

Psychopaths are biologically incapable of understanding why that’s wrong – it’s like asking someone who was born blind to grasp the concept of green. But even we can see that, according to your rules, going round slaughtering people isn’t going to win you any popularity contests.

But there are some exceptions to this rule, aren’t there?

Sometimes it’s OK to kill people.