Anti-paedophile vigilante Christopher Hunnisett who murdered a gay man he wrongly believed to be a child molester was told on Tuesday he may never be released from prison.
Hunnisett, 28, killed supermarket worker Peter Bick, 57, just four months after being freed from jail following his acquittal for a vicar's murder.
The judge described him as "an extremely dangerous man who may well kill again" as he was jailed for life with a minimum term of 18 years at Woolwich Crown Court.
Justice Saunders said: "The time may never come when this defendant is considered safe to be released."
Hunnisett previously spent more than nine years in jail for killing the Rev Ronald Glazebrook, 81, in his bath and cutting up his body in April 2001.
His conviction was quashed and he was cleared of Mr Glazebrook's murder at a retrial during which he alleged that the priest sexually abused him.
After being freed from prison in September 2010, Hunnisett, of Hastings, East Sussex, made a "hit list" of men he planned to kill in his bid to rid the world of paedophiles.
Having formulated a plan to track down child abusers and rapists while he was in custody, on his release he set up false internet accounts as a "honeytrap" for sex offenders.
Mr Bick, an Asda employee from Bexhill-on-Sea, East Sussex, was at the top of Hunnisett's list of targets, although the prosecution said there was "not a shred of evidence" that he was a paedophile.
Overnight on January 10-11 last year, Hunnisett had sex with Mr Bick at his flat before brutally smashing his head with five severe hammer blows and strangling him with a shoelace.
The killer tried to cover his tracks by sending text messages falsely suggesting that the supermarket worker believed he was meeting a 15-year-old boy.
Mr Justice Saunders said Hunnisett went to Mr Bick's flat prepared to kill him, and carried out a "planned and cold-blooded" attack.
He noted that the defendant had an "intense hatred" of paedophiles, having suffered abuse as a child.
The judge said: "He believes that the penalties handed out by the courts for child abuse are inadequate.
"For him the appropriate penalty, if he considers it necessary, is death. He has appointed himself judge, jury and executioner.
"However good the evidence of child abuse, the defendant was not entitled to take the law into his hands in the way he did but, as he demonstrated in this case, he was prepared to reach his conclusions on entirely inadequate evidence."
Mr Justice Saunders observed that Hunnisett's hatred of paedophiles grew during his time in prison, where he might have come into contact with sex offenders who showed a lack of remorse for the harm they committed.
He said: "The evidence that I have heard has driven me to the conclusion that the defendant is now an extremely dangerous man who may well kill again were he to be released in the foreseeable future."
David Martin-Sperry, mitigating, said that while in prison Hunnisett was forced to play the role of an abuse victim in therapy sessions organised for sex offenders.
He was then freed after being acquitted of Mr Glazebrook's murder without being prepared for his release and with no authority responsible for supervising him in the community.
Hunnisett, unshaven in a black and grey casual jacket, made no reaction as his sentence was passed, but mouthed a few words to family members in the public gallery as he was led away by court guards.
Following the case, Detective Chief Inspector Nick Sloan of the Surrey and Sussex Major Crime Team, said: "This was a terrible crime, and the jury were clearly unconvinced by Hunnisett's claims about his motives for carrying out such a cruel and deliberate killing.
"Peter Bick's sister, together with her husband, was present at court throughout the trial and they had to listen to Christopher Hunnisett deliver utterly unfounded personal attacks about the character of her brother.
"They endured this with great dignity and this is testimony to how they have conducted themselves since Peter was murdered.
"What exactly was motivating Hunnisett in the lead up to the murder and afterwards we will perhaps never really know, but there is no doubt at all that society is a safer place now that he is in prison."