I had a dwarf that turned out to be a vampire, and ended up being elected mayor. I walled them up in their spacious quarters for a while and assigned them as the bookkeeper. After a few years, I got bored of this, unwalled their quarters after locking them into one of the rooms in it, then moved a caged magma crab into the room and connected it to a lever. I locked the outside door, unlocked the inside door between the vampire and the cage, then pulled the lever. The vampire wandered into the room with the crab, and immediately started getting pelted by basalt. Unfortunately, after dozens of hits, he was mostly only taking bruises, and spending most of his time running between rooms while the crab chased him. Once or twice, the vampire would stop to grab the crab, and tore off a leg once. I decided to confine the vampire and the magma crab to the same room, and the vampire started to take more and more hits from the basalt the crab was spitting at it. Finally, the vampire had a tantrum and proceeded to tear the crab apart, killing it in short order. By this time the vampire had accumulated quite a good number of wounds, although nothing immediately life threatening. But about a minute after the magma crab died, the vampire had apparently had enough, and went berserk. Since he was now targetable to my military, I sent multiple squads to wait outside his door, then once a suitable number had amassed, opened the door and sent them in. The vampire fell pretty quickly after some taking some nice hits from my military, including getting two limbs cut off by an artifact adamantium axe. I was concerned briefly because there were various body parts strewn throughout the room, with a different name than the vampire. I feared that the vampire had torn one of the dwarves asunder, until I realized that upon his death, the vampire's true identity had been revealed. He was given a proper burial, to hopefully avoid any further problems from him, and his quarters were assigned to the new bookkeeper.