Jon Venables, one of the killers of toddler James Bulger, struggled to cope after his release from a secure children's home and was jailed for child pornography offences last year. The detective who handled the case believes the youth justice system failed Venables.
Venables, now aged 28, was 10 when he and friend Robert Thompson murdered the toddler in Bootle, Merseyside, in 1993.
Venables was sent to the Red Bank Home in Merseyside and Thompson to Barton Moss Secure Care Centre in Manchester.
They were given new identities and freed in 2001, when they turned 18.
"I'd hoped that they would be capable of being rehabilitated, but I never had the faith in the system where I believed they could achieve that by 18 years of age," Albert Kirby, the former Merseyside detective, said.
Thompson is not known to have reoffended since his release, but Venables's life spiralled out of control.
While at a vulnerable stage, Venables "had problems adjusting to trying to live a lie, failed to come to terms with what he'd done and make the adjustments to living outside after having no life experiences," said Mr Kirby.
Despite this, he was adept at presenting himself positively, and his supervision visits were reduced.
Mr Kirby said: "(With) supervision and contact slipping away and being eased off, that is the period when we know now that Jon Venables became vulnerable, his behaviour went out of control, and there wasn't the mechanism there, the system there that he felt he could go and feel happy with.
"That cannot be acceptable."
It costs about £215,000 a year to keep a child in one of the UK's 10 secure units. Their emphasis is not on punishment, but rather to rehabilitate within the confines of a secure setting and prepare for release. But there are no statistics on reoffending rates.
Child offenders go through intensive therapy to come to terms with and take responsibility for their crimes.
A former manager at Red Bank, Pam Hibbert, said: "Actually acknowledging their own responsibility, that's a really big hammer blow to children.
"'I did this, I really did this, I did something horrendous, that is vilified by the world'.
"It's a big thing and you have to be very tough with them and not let them make excuses. That's really important."
After Venables was released he was living in Cheshire but began visiting Merseyside, breaching a condition of his parole.
Mr Kirby said housing Venables in Cheshire had "put him too close to temptation".
Venables developed drugs and drinking problems, which initially went unnoticed by officials, began acting anti-socially, and while on two separate nights out, with a friend, told them he had committed the murder.
Later, he told his probation officer his cover story had been compromised, and the officer visited his home to find him destroying a computer hard drive.
It was found he had downloaded 102 indecent images of children and had been distributing indecent images as well. He was jailed for two years.
Mr Kirby said he had been detained because he was a risk to the public but no professional had realised that "he had presented this risk to himself".
"I've always believed the severity of what they [Venables and Thompson] did demanded a far greater sentence," said Mr Kirby.
"Bearing in mind the magnitude of what they did and the publicity surrounding the case, I always thought they couldn't come to terms with what they had done.
"There are other ways they could have been dealt with. I think all along there was a lots of misjudgement over Venables's suitability to be released.
"They could have gone into prison as a warning to them that if they ever did break the conditions of their parole, that's where they would end up.
"I think when you look at what we've learned, it raises big questions as to whether it was a matter that Jon Venables will be released, or whether he should actually be retained in custody, but perhaps in some other location."
James Bulger's mother, Denise Fergus, said Venables should be detained in prison indefinitely.
"We should learn from the past, you know, that it doesn't work giving them the best of everything, that it doesn't work rehabilitating them, it doesn't work spending a lot of money on them," she said.
But Mr Kirby said: "It's very wrong for any young person to go to any institution and not have the hope that one day they could be released."
Pam Hibbert said: "What do we want to do with these children who do commit very serious offences?
"Now some people would say we should lock them up and throw away the key, but if we believe that adults can be rehabilitated, surely we have to believe it for children?"
So could Jon Venables ever be fully rehabilitated?
Albert Kirby said: "I don't think at the moment he can be, I think the damage done by his reoffending means that now he will never be.
"There is no evidence he has abused children, but I don't think for him to end up indefinitely in a prison is the answer.
"He needs an institution where he receives mental health help."
Venables could be back on the streets in July 2011, though it will be up to the Parole Board to decide if he is ready.
He will remain on a life licence, so could be recalled to prison at any time, and his name will be added to the Sex Offenders' Register.
Jon Venables: What went wrong? is broadcast on Thursday at 2235 BST on BBC One