Convicted murderer asks TV show to prove his innocence but find evidence he, and others, were guilty

A convicted killer's plan to use a TV documentary to prove his innocence has backfired - as the investigation claims he may have helped cover up the involvement of others in the killing. 

David Szach was 19 years old in 1979 when he was charged with the murder of his 44-year-old lover, Adelaide lawyer Derrance Stevenson, with whom he had been living for three years.

Mr Stevenson was shot in the back of the head sometime between June 4 and 5 of that year. His body was found curled up in the fetal position, hidden in a freezer with the lid superglued shut.

David Szach was convicted of the murder on key evidence from South Australia's former chief forensic pathologist Colin Manock, who had no formal qualifications as a pathologist, and whose evidence in other cases has been discredited.

Mr Szach said he was innocent, but he lost his appeal against his murder conviction in 1980. He served his entire 14-year sentence.

Desperate to clear his name, Mr Szach approached Foxtel documentary show Frozen Lies to investigate his case.

The TV crew led by author Debi Marshall and former NSW Police forensics detective Kris Illingsworth reviewed the evidence for 18 months but came to a stunning conclusion.

Frozen Lies decided that Mr Szach had committed the murder - and that he had also likely covered up the involvement of others, News Corp reported.

'I did not kill Derrance Stevenson, I played no part whatsoever in his murder,' Mr Szach told Foxtel.

Mr Szach said he had no reason to lie.

'That is your ending it's not my ending,' he said as he walked off the set.