Well, the "murder" (I can't really call it that, the second court did some awesome mental and legal gymnastics to get a murder charge instead of a manslaughter charge) wasn't done from sexual motivation on ther perps part, but the VICTIM was sexually motivated to get killed. The guy killing him then got satisfaction from the butchering (well, watching the butchering on tape, afaik he said the dismembering itself didn't turn him on, his fantasy was watching it getting done) and the eating.
It's a pretty gruesome story, featuring two individuals that are, from a layman's perspective, pretty ill and should have gotten therapy instead of acting on their urges.
But I'm no psychologist and of course, self determination is an important right. I won't judge somebody for fantasizing about getting his penis eaten, but I sure would tell him to seek professional help.