Serial killer John George Haigh knew the power of the monstrous image to incite horror into people's minds, and even today he is cited as a murderer who drank a cup of blood from his victims before getting rid of their bodies. He's found on nearly every list of "modern vampires," which attests to his own insight in just how far his legend would carry. However, there's no evidence that he had such a fetish and plenty of reason to believe that he was malingering a mental illness that would get him sent to a mental institution.
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.

i was going to suggest that he may have had poryphria but after reading this i dont think he did. he may have a disorder of some sort or was just wanting his 15 min of fame...

Psychiatrists do not have the ability to tell if a person has a certain fetish or compulsion. What if he had it during that time, then passed? What if he was truely psychotic, but could pretend he was normal for a short time. There are infinate possibilities, especially when it comes to the human brain. When one believes something truely and enough, the body believes it, and some people go crazy, truely believing that they're something they are not.