Why do we read books about murderers? While reading this one in public, I kept feeling a guilty urge to conceal its front cover. I don’t want people thinking I’d read a book about Martin Bryant for fun. If I must be caught reading about a killer, I’d sooner it was someone like the Unabomber or Lee Harvey Oswald. Their crimes were American, for a start, which puts a sort of protective veil over the horror of what they did. And there’s a bit of nuance in their stories, a bit of texture: a flash or two of criminal ingenuity,…