The Vampire Killers
When he was arrested in England in 1949 for the possible murder of a missing woman, Haigh's first question concerned his chances of getting out of the local mental institution. Quite soon he launched into a detailed confession that involved killing six people in order to drink their blood. He said that he lured them into a storage area and then hit them over the head to kill them. Then he would cut open an artery in their throat and fill a cup with blood to drink it: Imbibing fresh blood made him feel better. Then he would dissolve the corpse in large drums filled with acid. He had to do this, he claimed. He couldn't help himself
However, there's clear evidence that each crime was committed when Haigh was in debt and there's no evidence that he acted under a compulsion. In fact, 12 physicians examined him and only one thought he had an aberrant mental condition—egocentric paranoia. The others believed that he was making it all up.
It appears to have been a ploy to shock the public into accepting that he could only be mentally ill so that he might avoid the death penalty. He had posed before as a doctor, a lawyer, and an engineer when it suited his purposes. In this case, he posed as a psychotic person who drank blood.
But it didn't work. As he awaited his execution in prison, three more psychiatrists examined him and they still could find no evidence that he had a blood-drinking compulsion.
While it was unlikely that Haigh was psychotic when he killed his victims, there are some whose psychotic manifestations are indeed directed by what they know about vampires. Let's take a look.