I remember one of my forts that was dedicated to researching cages as life support devices for insane dwarves.
I had a lot of war dogs bred, and whenever my justice system ended up choosing a new prisoner to punish for the mandates I intentionally broke, I assigned twelve dogs to said prisoner. I then killed the dogs one by one, with weeks passing in between deaths, until the poor soul finally went mad.
Once that happened, I had the prisoner's cage deconstructed and put into a special burrow, which I named "Asylum", where twelve useless migrants were isolated from the rest of the fort; they were to feed and water the prisoner and had no other tasks. Despite their clear and concise job description, the wardens still managed to let their wards die.
After my eleventh test subject had expired at the hands of these incompetents, I grew weary of their constant failures and decided to abort the project. I took one of my captured vampires, threw his cage into the asylum and walled it off. Then I had the vampire released.
In four days, one of the migrants was found dead. Fifteen more, and another warden was drained of blood. Every time a migrant went to sleep, there was a good chance the vampire would take their life. Soon, the migrants' nerves started to fail, and they showed signs of approaching madness: mindless vandalism, agressive behavior and lethal food fights. While throwing a tantrum, one of them took down the locked doors of the asylum... only to see a newly-erected block wall in place of the familiar corridor. He was brained by a flying piece of egg roast several days later.
Those wardens who lived the longest started going insane as the booze ran out. The ninth warden to die went berserk and attacked the vampire, breaking his left arm and shattering his toenail before the vampire bashed his head in. The tenth succumbed to melancholy and drowned himself in the well. The eleventh was drained of blood, and the twelfth started babbling once he tasted the tainted waters of the well; he died of thirst soon after.
Nine months after the asylum was sealed, the dwarves from my main fortress took down the wall. Inside, they found rotting corpses of the wardens and a vampire, who was still saddened by the deaths of his newfound friends. He took the blame for most of the murders and was sentenced to several years in prison. Despite his immortality, the vampire did not live to taste freedom again: the untreated infection from his toenail killed him the next year.