Andrew Allder was found guilty of the stabbing of shop assistant Kathleen Turner in Kingsbury in 1987 when he was 17 years old. He spent 17 years in prison before being released three years ago – but could have been freed earlier if he had admitted to the crime. However, he always maintained his innocence.

Campbell Malone, who helped free Stefan Kiszko, the man wrongly convicted of the sexual assault and murder of 11-year-old Lesley Molseed in the 1970s, has now come on board at the request of campaign group Innocent, which is backing Allder's case.

Allder, 37, who lives in Blackpool with his wife Gaynor, told The Bucks Herald: "Campell Malone is a very good lawyer, and very thorough. I have met him once so far but had numerous phone calls with him. I think the first visit was to weigh me up and hear what I had to say. He's a very professional man."

The Criminal Cases Review Commission is looking at his case, and will eventually make a decision on whether it gets referred to the Court of Appeal.

Allder, 37, hopes the decision will be made by the end of the year.

"I've got this feeling in my heart that this is the 20th year now and it will be the year that the CCRC will take my case to court," he said. "It's not about getting out now – although I would have loved to have walked out of prison a free man. It's all about clearing my name, which means everything to me."

Andrew Green, Allder's caseworker from Innocent, said: "Campbell Malone is the right person to handle a case like this. There is no more experienced appeals lawyer than him."

Mrs Turner, who was 67 and employed at Dennis's Aylesbury Leather and Travel Goods, died from a single knife wound to the back as she worked in the shop alone. There were no witnesses to the murder.

Allder voluntarily went to Aylesbury Police Station to eliminate himself from the enquiries, after hearing that detectives were looking for a young man matching his description seen running from the scene.

During interview he signed a confession to the crime and was jailed in 1988.