Professor Paul Mullen

These are lonely, isolated, forgotten people in a way.

They're almost all white.

Very few of these killers come from any other background than a relatively prosperous society.

a white middle-class background.

They are not abused children.

They don't have a history of severe sexual abuse.

Interesting.

They're just these odd, isolated kids.

Their intelligence levels vary, so it's not about intelligence.

And it's not about poverty and abuse, which most crime is about, actually.

So what is it?

Well, these are people who believe they have failed in life despite having really great abilities.

And they have a deep resentment against the world in general.

And they become hopeless about their lives.

And at some point, they start contemplating suicide as a way out of this.

Now, they have some other features.

Most of them are fantasists.

And what fantasies have they tend to favour?

Military glory.

It's remarkable how many of these people have tried to apply to the police or to the military and been turned down.