Ian McLoughlin, who today admitted to the murder of pensioner Graham Buck, had killed twice before.
In 1984, he hit Len Delgatty, 49, over the head with a hammer several times after a row, and left his body in a cupboard. He was jailed for 10 years for manslaughter at the Old Bailey, reduced to eight years on appeal.
After his release, he went to live in Brighton, where barman Peter Halls, 55, offered him work. McLoughlin said he assumed Mr Halls was gay, and thought that he may be expected to sleep with him.
McLoughlin stabbed Mr Halls several times, and in 1992 was jailed for 25 years for murder, serving a total of 21 years behind bars.
Ian McLoughlin, who today admitted to the murder of a pensioner, said in a police interview he was "sorry" for the killing but did not regret the initial robbery.
McLoughlin, 55, who will be sentenced this afternoon, had met convicted paedophile Francis Cory-Wright in prison and turned up to his house claiming to need help setting up a charity supporting elderly ex-offenders.
But the 55-year-old, already a convicted killer, grabbed Mr Cory-Wright and demanded to know where he kept his "gold and silver".
The convicted paedophile, who was jailed for 30 months in 2011 for indecently assaulting a 10-year old boy in the 1970s, was tied to his bed and McLoughlin put silver family heirlooms into a pillowcase and demanded his bank cards and pin numbers.
Father-of-three Graham Buck, who lived two doors away from Mr Cory-Wright, went to help him after hearing shouting in his front garden.
McLoughlin said he was confronted by Mr Buck as he tried to flee the house and stabbed him.
Triple killer Ian McLoughlin has been jailed for life with a minimum of 40 years at the Old Bailey for the murder of Graham Buck, 66, who was stabbed when he went to the aid of his convicted paedophile neighbour during a robbery.