Much of Britain is currently following the trial of Steven Griffiths, or as he'd like you to refer to him, the Crossbow Cannibal.
Serial killers are always newsworthy, and Griffiths has killed at least three women in cold blood. (He did use a crossbow, but I think the newspapers made up the cannibalism.) But it's Griffiths's interests that have really got people's attention.
It turns out that before he became a serial killer, he was a man obsessed with... serial killers. His Amazon wish list was full of books about murder. He has a degree in psychology, and he was working on his PhD, in Criminology. Guess what his research was about.
Griffiths is therefore a kind of real life Hannibal Lecter or Dexter, an expert in murderers who is himself one. He's also a good example of the fact that, unlike on TV, real life serial killers are never cool and sophisticated, nor even charmingly eccentric, just weird and pathetic. Not to mention lazy, given that he was still working on his PhD after 6 years...
Yet there is an interesting question: was Griffiths a good criminologist? Does he have a unique insight into serial killers? We'll probably never know, at least not until (or if) the police release some of his writings. But it seems to me that he might have done.
When the average person hears about the crimes of someone like Griffiths, we are not just shocked but confused - it seems incomprehensible. I can understand why someone would want to rob me for my wallet, because I like money too. I can understand how one guy might kill another in a drunken fight, because I've been drunk too. Of course this doesn't mean I condone either crime, but they don't leave me scratching my head; I can see how it happens.
I cannot begin to understand why Griffiths did what he did. My understanding of humanity doesn't cover him. But he is human, so all that really means is that my understanding is limited. Someone understands people like Griffiths, it can't be impossible; but it may be that the only way to understand a serial killer is to be one.
The same may be true of less dramatic mental disorders. Karl Jaspers believed that the hallmark of severe mental illness is symptoms that are impossible to understand: they just exist. I've experienced depression; I've also read an awful lot about it and published academic papers on it. My own illness taught me much more about depression than my reading. Maybe I've been reading the wrong things. I don't think so.