Leslie Bailey, who was serving three life sentences for his part in the killing of three boys abducted by a group of paedophile sadists, was found dead by prison officers at Whitemoor Prison, Cambridgeshire.
Inmates, including convicted killers and IRA terrorists, were being interviewed by police, who are treating the death as 'suspicious'.
Investigations are under way at the prison and the Home Office to discover how a 'vulnerable' prisoner in a segregated wing could die in such a way.
Detective Superintendent Bob Wordsworth said: 'At this time we are holding an open inquiry and we are questioning staff and inmates to try to ascertain when he was last seen alive. The possibility of a self-inflicted injury has not been ruled out.' Asked if he thought Bailey's death was rough justice, Det Supt Wordsworth said: 'I am a police officer and I uphold the law and in my view no one has the right to kill anyone.'
Bailey, 40, was found dead in his cell on Thursday night when warders made their lock-up checks just before 8.30pm. He was discovered lying on his bed; a post-mortem examination revealed he had been strangled.
Andrew Barclay, the prison governor, said Bailey had been threatened during his time at the jail and as a result was held in a special wing along with other vulnerable inmates.
Segregated prisoners eat and socialise separately and Bailey was on his own in a cell during evening association time. Mr Barclay said inmates within the wing could visit other cells.
He said that despite having been threatened, Bailey had been quite settled over the last few months. 'As part of our inquiry we will try to find out if he had demonstrated any suicidal or depressive signs.'
Bailey was convicted as a result of Britain's biggest child murder hunt, codenamed Operation Orchid, which investigated the disappearance of several boys since 1980.
It lifted the lid on a seedy underworld of rent-boys, paedophile rings, drugs, homosexual orgies and ultimately child murder. One detective described it as 'perversion in the ultimate form'.
Bailey was jailed in 1989, along with three other men, for killing Jason Swift, a 14-year-old rent boy who had run away from home. He died from strangulation after being drugged during a homosexual orgy. Bailey was found guilty of attempting to choke him.
A social inadequate of less than average intelligence, Bailey was nicknamed 'Catweasel' because of his thin features and staring eyes.
The case led police to investigate the alleged existence of so-called 'snuff' movies in which, it was claimed, children were lured to parties and filmed being abused and killed. Detectives feared that up to 25 children might have been abducted and further inquiries led to Bailey's conviction in 1991 for the murder of Barry Lewis, aged six, in 1985.
Bailey admitted strangling Barry after a homosexual orgy. The boy had been snatched from the street and taken to a a flat in Hackney, east London, where he was drugged, stripped and sexually assaulted by seven or eight men.
Believing the boy to be dead, Bailey put him in his car and drove to Essex intending to dispose of the body. The boy stirred, however, and Bailey strangled him before burying his body.
As Bailey was beginning his life sentence he told a cellmate about the death of seven-year-old Mark Tildesley, who disappeared while visiting a fair in Wokingham, Berkshire, in 1984.
The information was passed to detectives at Scotland Yard, and last October Bailey received two further life sentences for the killing. The judge at Reading Crown Court told him his cruelty to the boy had been 'absolutely despicable'.
Mark Tildesley's father, John, said yesterday that he would like to congratulate Bailey's killer. 'If I found out who strangled him I would shake hands with him. Whoever did it, did a good job. They saved the Government and the taxpayers a lot of money.'