The man, Colin Hatch, 21, who is unemployed, had a series of previous convictions for offences against young boys dating back to when he was 15, the court was told.
Hatch was jailed for three- and-a-half years in December 1991 for indecently assaulting and falsely imprisoning an eight-year-old boy - but released on parole in April 1993. The body of Sean Williams was found wrapped in bin liners in a lift near Hatch's home on 19 July that year. Hatch, of Finchley, north London, has admitted Sean's manslaughter, but denies murdering him.
Detective Inspector Ronald Laverick told the court that Hatch had confessed that he panicked after abusing Sean in his bedroom. Hatch allegedly told officers he grabbed Sean by the throat as the boy went to the window to shout for help. Hatch also told officers after his arrest that he did not kill to get further sexual gratification.
'I did not expect to kill him. I thought it would be the same as the other offences, but then it just got out of hand,' Hatch allegedly told officers.
Details of Hatch's previous convictions were outlined in court by Lawrence Kershon QC, for the defence, and confirmed by Mr Laverick. In the last assault, Hatch had approached his eight-year-old victim on a housing estate in south London, where he was living at the time. Hatch took the boy into a room in a block of flats and forced him on to a mattress. To stop him screaming, he put his hand over the boy's mouth and another round his throat, which made the boy lose consciousness. Hatch later released the boy.
When arrested, Hatch admitted the assault and said he could not stop himself carrying out sex attacks on children. He had also been sentenced on three other occasions for assaults on young boys.
Mr Laverick said that when questioned about Sean's death, Hatch told him Sean had come to the entrance of the block of flats where Hatch lived looking for another boy. Hatch led him inside his own flat, where the offence took place.
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