John George Haigh appeared a respectable, neat, middle-class man. But behind that façade lurked a psychopathic killer who would change British criminal history.
From mild beginnings as a petty fraudster, his crimes escalated to make him one of the nation's most notorious serial killers, who dissolved his victims in vats of acid.
Now for the first time, letters written by Haigh are to be made available to the public, giving an insight into the mind of a multiple murderer.
Haigh, dubbed the "acid bath vampire" by the media after he claimed in court that he drank his victims' blood, was convicted of the murders of six people during the 1940s. And he confessed to killing as many as nine.
Researchers now hope that by studying the letters, donated to Cambridge University's Institute of Criminology, they can learn more about what motivates serial killers and how to treat psychopaths.
Haigh's killing spree began in 1944, after his release from prison where he was serving time for theft. After killing a former friend, William McSwann and his wealthy parents, he dumped them in 40-gallon drums, immersing their bodies in sulphuric acid until they turned to sludge. He poured the remains down a manhole. Haigh then stole his victims' pension cheques, sold their properties and moved into a hotel in Kensington.
By 1947 he had gambled away the money and, in need of funds, he lured new victims. First Dr Archibald Henderson and his wife Rose were shot and dissolved. Then in 1949, he murdered a wealthy widow, Olive Durand-Deacon.
Police became suspicious while questioning Haigh and further investigation led them to his workshop in Crawley. There they found pools of sludge containing some of Ms Durand-Deacon's remains: fat, part of her left foot and dentures. Forensic tests were carried out, and Haigh was arrested, tried and imprisoned. He was sent to the gallows in August 1949.
Professor Friedrich Lösel, director of the Institute of Criminology at Cambridge, said: "What is fascinating is that he shows a number of symptoms that we find in patients who have psychopathy: He shows no remorse, no signs of guilt or self-reflection. He also exhibits delusions of grandeur - he is proud to read about himself in the papers."
The collection also includes school essays and business cards from his ill-fated enterprises.
Researchers increasingly believe that psychopathy is the result of a neurological defect in the brain that prevents the person from understanding the emotional or moral impact of their actions.
The collection was donated by Vivian Robinson, whose grandfather helped Haigh's parents to cope with their son's criminality.