Fresh DNA evidence was key to finding Dieter Pfennig guilty of murdering Adelaide schoolgirl Louise Bell but he has now won permission to appeal the conviction after questioning the validity of that very evidence.
Pfennig, 68, was last year convicted of abducting and killing 10-year-old Louise, who was snatched through her bedroom window in Hackham West more than 30 years ago.
Louise's disappearance in 1983 sparked a police search of unprecedented scale in suburban Adelaide. Her body has never been found.
Pfennig was arrested in 2013 when DNA scientists in the Netherlands linked him to the girl's pyjama top, which was found folded on a neighbour's lawn.
He was tried for murder by a judge alone, found guilty and sentenced in the Supreme Court to at least 35 years in prison, seemingly putting an end to the long-running cold case.
But the former science teacher sought leave to appeal against the guilty verdict, questioning the validity of the DNA evidence.
He claimed the prosecution evidence didn't rule out the possibility that his DNA could have been innocently transferred to the pyjama top.
Defence lawyer Paul Chapman said this transfer could have been through Pfennig's daughter, who went to school with Louise and played on the same basketball team.
The Court of Criminal Appeal delivered its decision on Tuesday, granting Pfennig permission to appeal against the conviction.
"I grant permission to the applicant to appeal on the ground that the verdict is unreasonable or incapable of being supported having regard to the evidence," Justice Malcolm Blue said in his judgment.
Prosecutors have previously discounted the involvement of Pfennig's daughter, saying she was not close friends with Louise and the last known contact was before the pyjamas were bought.
Pfennig's appeal will be heard by the Full Court on a date to be set.