I'm thinking of running a Special Investigation based game once I grok the rules well enough and I think the characters first case will be catching a serial killer who takes their victims heads with him. I'm toying with the idea of them discovering that it really is a mundane psycho this time but even if that's what I go with I need some good red herrings for them to chase. What in the Dresden verse would collect peoples heads and why?

I suppose a Necromancer might take the heads away so they can be questioned (perhaps for bank account information) or simply tortured for fun . . .

Any other ideas?