Solicitor Laurence Lee said at first he could not believe the "angelic-looking" Jon Venables could possibly have carried out such a brutal and sadistic killing.
But "the walls came crashing in" soon into his client's police interviews when it became clear that Venables had been lying and that he had in fact carried out the killing with his friend Robert Thompson, also then aged 10.
Mr Lee represented the then 10-year-old Venables from the moment his client was arrested by police on February 18, 1993.
Describing his first meeting with Venables, Mr Lee, who now runs his own law firm in Liverpool, said: "He was like an angelic-looking eight-year-old. I thought 'what am I doing here? He couldn't be capable of anything like this'. He was so convincing in his first interview that he had been nowhere near the Strand."
Venables claimed that he had been on County Road, near Goodison Park, with Thompson but said neither of them had been at the shopping centre where the toddler went missing.
Mr Lee, 59, said: "And I believed him. He was convincing. And it was only after there was a time-out and the officers who interviewed Thompson had a briefing and came back for the second interview.
"And again I was in blissful ignorance thinking, it's the easiest money - I felt guilty, actually, because this boy had had nothing to do with anything, I thought - until having got him cosy with his little space pens and his can of Coke, they kept him nice and relaxed and they said 'look we've spoken to Robert and he says you were in The Strand'."
After a silence Venables responded: "Well, ok, we were in the Strand but we never grabbed a kid."
Mr Lee said: "He got up and he grabbed his mum and he was crying and I thought 'oh my God, what have I let myself in for here?'
"The walls came crashing in at that moment and I knew what he was like and it was...God it was like a living nightmare."
He said he was "caught up in a maelstrom of massive criminology" and it was something he could not have prepared for.
"It was the kind of case that no solicitor had ever dealt with. I was in my 30s and I had never dealt with anything like this before."
When he was led out of that second interview, police had to check his car as he was a possible target for reprisals.
He said: "I had never been in this position before. I thought I was going to get assassinated or something at first because the public's feelings - including my own - were running high."
Mr Lee said from then on it was extremely difficult getting instructions from the young Venables.
He said that he and junior defence barrister Richard Isaacson would sit with Venables at Red Bank secure unit in St Helens, Merseyside, playing Tetris on Nintendo Gameboys and trying to get him relaxed enough to talk openly and "eke information" out of him.
But Venables had "mentally shut down" by that point, Mr Lee said.
The lawyer said one of the hardest parts of the case was looking after Venables' parents who he described as "very respectable people who were going through a nightmare".
"They were good people. Lovely people. They didn't have a clue what was happening," he said.
Mr Lee said as far as Venables was concerned his background was "no worse than any kid in Liverpool" and at the time he had actually been given a responsibility by his schoolteacher.
Mr Lee said: "He was on his way to pick up the gerbils from the school and it was only because he bumped into Thompson who said, 'forget the gerbils, lets go robbin'."
He added: "Thompson had this kind of hold. He was like the Pied Piper."
Venables claimed that he was an unwilling participant in the attack.
But Mr Lee said the "terrible injuries suffered by that poor child" could not have been carried out by just one of them.
Remembering the trial, which was held in Preston Crown Court, Mr Lee said: "They couldn't have found a more daunting venue than court one at Preston. It is scary."
He said they had to raise the dock by 18 inches so the defendants could see over the top of the rails.
Despite being Venables' defence solicitor he said he would have "happily" prosecuted the case against them and said his heart always went out to the Bulger family.
"My number one sentiment is for Denise (James' mother) - still is and always will be. The wounds re-open for that lady every time this comes up and now must be horrendous for her."
He said he was shocked that Venables, who was jailed in 2010 for downloading child pornography, had re-offended and that Thompson had managed to stay "under the radar".
He added: "Venables couldn't handle being out. He was always looking over his shoulder.
"They may be at liberty but they will never be free. And Venables may have had his liberty but he was never free; couldn't handle it and I think it was almost a cry for help from him to get remanded back into custody."
Mr Lee, who has not seen Venables since 1994, said he "does not want to know" Venables.
Mr Lee said the Bulger case was a life changing event for him, which he said made him ill for some time after the trial.
He added: "We are all human beings and everybody was affected by it. Nobody with any heart could have failed to have been affected by that case."
Ralph Bulger, James' father, is releasing a new book called My James which will be published ahead of the 20-year anniversary of the murder next Tuesday.
In comments published at the weekend, he spoke of how in his darkest moments he blamed Denise for letting their son out of her sight - a reaction which now makes him feel deeply ashamed.
He also spoke about how he downed two bottles of whisky a day to blot out the pain... and how he thought about killing himself in the wake of the tragedy.
Speaking about the end of the trial he said: "I thought I was going to combust on the spot. It was the right result. It meant my son's killers were going to be punished. But I didn't feel euphoric. I leaned in slowly and kissed Denise on the cheek. 'We got them', I whispered.
"What we didn't realise then was that the spotlight would never leave this case, and that so much more was to come."
It was a grainy CCTV image that appeared to show an innocent scene of a toddler walking hand-in-hand with a child.
But what the pictures in fact revealed turned out to be every parent's worst nightmare.
As James Bulger was led through the Strand shopping centre in Bootle, Merseyside, on February 12 1993, there was nothing to hint at the dreadful murder he would later suffer.
Moments earlier he had been seen on cameras walking with his mother Denise Bulger, now known as Denise Fergus.
Although occasionally dropping a few steps back, he followed his mother into a shop.
A short time later he was seen leaving alone, with his mother in pursuit soon after.
But instead of finding her son wandering nearby, it soon became apparent that James was missing.
The next day, his parents, Denise and Ralph, made an emotional appeal for help as detectives released CCTV images that would shock the nation.
They revealed the terrible reality that James had been abducted - by a child.
For reasons that are still unknown, Jon Venables and Robert Thompson, then aged 10, had led the toddler out of the shopping centre.
Shocking details of James's torture would later emerge during the trial.
The two boys, who were truanting from school, walked James around the streets of Liverpool for more than two miles, stopping occasionally to kick and punch him.
They told adults who intervened that he was their brother.
After taking him to a nearby railway line, they left his body on the tracks in the hope it would be destroyed by a train.
The toddler had been splattered with blue paint and his battered head lay surrounded by a pile of bricks.
His body was found two days later by children playing on a freight railway line - 200 yards from Walton Lane police station, Liverpool, and more than two miles from the Strand shopping centre.
Days later Venables and Thompson were arrested in connection with the murder of James, and later charged.
They were the youngest to be charged with murder in the 20th century.
In November that year, they were convicted following a 17-day trial at Preston Crown Court and ordered to be detained at Her Majesty's pleasure, the normal substitute sentence for life imprisonment when the offender is a juvenile.
Trial judge Mr Justice Morland told the pair they had committed a crime of "unparalleled evil and barbarity".
As shadow home secretary in 1993, future prime minister Tony Blair described the murder as "a hammer blow against the sleeping conscience of the nation".
Some 17 years later the country was awoken once again when Venables was returned to custody after allegedly breaching the terms of his release.
But details of his alleged crime were slow to emerge.
He had been controversially freed from prison in 2001 with a new identity, along with Thompson.
When they were released they were considered to be at serious risk of revenge attacks.
Dame Elizabeth Butler-Sloss, of the High Court Family Division, made an unprecedented court order banning publication of any information which could lead to the revelation of their new identities.
It was the court injunction preventing Venables's identification which meant details of the alleged breach were not immediately released.
The Ministry of Justice said the 27-year-old had been returned to custody "following a breach of licence conditions", adding: "There is a worldwide injunction in place that prohibits any reporting, including reporting on the internet, that could identify him or his location."
The Government faced growing calls to provide more information, including from the toddler's mother, Denise Fergus.
She said: "I am sick of them closing doors in my face. It's about time they started telling me what I think I should know. As James's mother I have a right to know."
But then-justice secretary Jack Straw said revealing further details would not be in the interests of justice.
Information about Venables's alleged crime could have led to his identification, putting Mr Straw in contempt of court.
The Attorney General's department issued a warning about the danger of publishing details which might make a fair trial impossible.
Lady Butler-Sloss herself stressed "the enormous importance of protecting his anonymity now and if he is released because those who wanted to kill him in 2001 are likely to be out there now".
Meanwhile, Mr Straw told the Commons: "If any offender on a life licence is charged with a serious further offence, a thorough review of the supervision must be carried out."
It later emerged a psychiatric assessment of Venables compiled prior to his release said he posed only a "trivial" risk to the public.
The account reportedly formed part of the legal case for Venables's release under a new identity.
On April 16 prosecutors were handed a police file over the allegations against Venables.
Despite news reports alleging he had been found with child sex abuse images on his computer, ministers were still only confirming that he faced "serious allegations".
It was not until June 21 2010, after a judge at the Old Bailey lifted media restrictions, that it could be reported Venables had been charged with downloading and distributing indecent images of children.
He was jailed for two years after pleading guilty to the charges and in 2011 he was refused parole.
Venables is expected to make a renewed bid for parole later this year.