We don't know whether he's mentally ill, but odds are he isn't. Indeed, criminologists and psychiatrists will tell you that most mass murderers aren't insane. But the public debate is already caught up in a familiar tautology. What Mr. Holmes did was an act of madness, therefore he must be a madman. And if he's a madman, we can't execute him because he's not responsible for his actions. And if he's not responsible, then "society" must be. And we can't execute a man for society's sins. So: Cue the debate about guns, and funding for mental health, and the popular culture.