A man living near Ipswich with severe learning difficulties who was convicted of shooting dead a shopkeeper said he was "put under pressure" to confess to a crime he didn't commit.
Oliver Campbell, who sustained a brain injury as a child, spent 11 years in various prisons after a jury found him guilty in 1991 of shooting dead Baldev Hoondle in Hackney.
A reported confession during police interview was used as a key part of the evidence to convict the 50-year-old, who has lived in Suffolk ever since finishing his jail term at Hollesley Bay Prison, near Woodbridge.
Yet there has long been doubt cast over his guilty verdict, with Mr Campbell’s solicitor, Glyn Maddocks, and barrister, Michael Birnbaum QC, saying: “Much of the police questioning was misleading and unfair.”
Now a BBC Newsnight film has raised further questions over his conviction, with Mr Campbell - who is still on licence for the offence - saying: "I was put under pressure to say things I didn't want to say."
In the programme, tapes from Mr Campbell's police interview are played in which he says: "I, I like pulled the trigger by accident.
"I said I pulled it, I was the one like pulled the gun on him and shot him."
However Stephen Mullinger, Mr Campbell's solicitor at the time, told Newsnight he was not present for the interview and that Mr Campbell did not have legal representation.
A judge ruled the confession as admissible in court - but his legal team argue the so-called admission of guilt should have been discounted, given Mr Campbell's severe learning difficulties.
Mr Birnbaum, who is also interviewed in the show, said: "Oliver is mentally very challenged and the police behaved, I think, very unfairly.
"The law and practice in regard to the way that mentally challenged suspects and defendants are treated has changed very considerably in their favour."
The Metropolitan Police, who conducted the interview, said in a statement: "The case was fully investigated at the time with a range of evidence brought before a jury who convicted the defendant in 1991.
"We are aware this matter is with the Criminal Cases Review Commission and therefore it would not be appropriate to comment further at this stage."
The case is currently being examined by the CCRC, which will decide whether or not there is enough evidence to refer the case to the Court of Appeal.
It rejected a previous appeal several years ago, despite the BBC's Rough Justice programme in 2002 bringing in a ballistics expert in 2002, amid claims of a lack of forensic evidence.
More than 80,000 people have since signed a petition calling for the conviction to be quashed, with Mr Campbell saying in an interview with this newspaper: "I went into prison innocent, I came out innocent and I've been innocent all the way through."
He has vowed to leave the country should he guilty verdict be overturned, saying the conviction has ruined his life.
Former Ipswich MP Sandy Martin also told Parliament that “Oliver simply was not capable of carrying out such a crime”, while Labour MP Barry Sheerman has urged parliamentary colleagues to sign an Early Day Motion backing the campaign.
Early Day Motions are signed by MPs to draw attention to certain issues.
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