I've heard of similar things in rape cases in documentary programs and stuff i've watched over the years. (one particular case that I seem to remember was of a young boy who raped and killed a female child and inserted sticks inside her after the attack). Stuff like that has also been referenced in certain crime programs over the years (I think 'cracker' with Robbie Coltrane was one of them)
I'm no psychologist, but from reading, I gather that at least in SOME of the cases like that, it's like an act revenge in a way. A kind of 'closure'. The idea that some of these women hating men feel like her vagina gives her so much power - the source of their pain, amplified in cases of unrequited lust. The want to degrade and destroy it