By now you must have heard of Josef Fritzl, the Austrian man who imprisoned and raped his daughter Elisabeth for twenty-four years. If you haven't, the Wikipedia page will give you the details.
I figured that if I rolled through my bookmarks for Theodore Dalrymple's favorite haunts, I would find his commentary on the case. After all, how could he resist? My diligence was rewarded when I found this article in the New English Review. Dalrymple sensibly concludes that we shouldn't expect ourselves to be able to understand why someone does such terrible things.