I finally identified my resident vampire. He was a migrant bone doctor that came in my second wave. After the hammerer refused to carry out the beating he was sentenced to, I locked him in his room. D'oh, vampires don't eat or drink. Oh well, I'll dig a pit above his room and fill it with water bucket by bucket. D'oh, vampires don't breathe. Fine, I'll crash the damn ceiling in on his head.
After ensuring that there was no one below my hastily-constructed crushing platform, I designate the support to be removed. It's physically impossible for dwarves to fit under the crusher. Yet three of them managed it somehow. Two died. The last, a mother with a child, survived the three-floor fall.
Oh, and I took out the vampire.