Former Jetstar pilot Greg Lynn has smiled as he learnt he will face a fresh trial after successfully challenging his conviction.

Three appeal judges on Thursday found Lynn, 59, had faced a “substantial miscarriage of justice” and ordered his murder conviction be set aside.

They found Lynn’s lawyers had proven several irregularities in his 2024 jury trial over the deaths of missing campers Carol Clay, 73, and Russell Hill, 74.

The pair disappeared from a remote campsite in Victoria’s High Country, where Lynn was also camping, in March 2020.

Lynn was initially charged with the two murders. He took the case to trial, where he admitted burning the bodies of Clay and Hill, but claimed their deaths were accidental.

The jury delivered a split verdict. Lynn was convicted of Clay’s murder and acquitted of Hill’s.

He appealed the murder conviction and 32-year prison sentence at a two-day hearing, where his lawyers argued it was an unsafe verdict as prosecutors put forward an “unfair” case.

His barrister Dermot Dann KC accused trial prosecutor Daniel Porceddu of having “chickened out” during his cross-examination of Lynn, who gave evidence at the end of his trial.

“The prosecution broke the rules from start to finish,” Dann told the appeal judges.

Lynn was convicted of the murder of Carol Clay, but acquitted over Russell Hill’s death.

Victoria’s Director of Public Prosecutions Brendan Kissane argued the trial was not conducted unfairly, defending his prosecutor’s handling of the case.

He submitted the defence should have applied to discharge the jury in Lynn’s trial at the time, if it was unfair.

On Thursday, Lynn clutched a folder and waved at his son Geordie as he entered the dock at the back of the Court of Appeal in Melbourne.

Court president Justice Karin Emerton delivered the three judges’ finding in a brief hearing.

“There were a number of serious irregularities in the course of the trial that were not capable of being remedied by direction and gave rise to a substantial miscarriage of justice,” she said.

“Mr Lynn’s conviction for the murder of Carol Clay will be set aside, and a new trial will be ordered.”

In written reasons published after the hearing, the judges said the prosecution’s conduct had “so compromised the fairness of the trial that there was a substantial miscarriage of justice”.

They said prosecutors had breached the rules of fairness in their closing address to the jury by challenging the credibility of Lynn’s evidence without ever putting it to him when he was a witness.

“The matters the subject of those breaches, including as to Mr Lynn’s post-offence conduct and his version of the events surrounding the shooting of Mrs Clay, were important to the case against Mr Lynn and he should have been given an opportunity to respond to them,” the appeal judges found.

They accused Porceddu of having “unfairly attacked” the reliability and credibility of the prosecution’s own firearms expert witness Paul Griffiths, without giving him a chance to respond.

Griffiths had conducted gunshot trajectory tests on Lynn’s account of what had occurred when Clay was shot, and had agreed the accused killer’s version of events was plausible or “spot on”.

“Yet prosecuting counsel invited the jury to disregard Mr Griffiths’ evidence entirely as ‘total speculation’ without a proper evidentiary basis for doing so,” they said.

They found these breaches were “sufficiently frequent” and could have affected the outcome of the trial.

A spokeswoman for Victoria’s Office of Public Prosecutions would not comment.

Clay’s daughter Emma Davies and Hill’s daughters, Deborah and Colleen, appeared emotional in court as the decision was handed down on Thursday.

Lynn was remanded in custody and will face the Supreme Court for a directions hearing on January 28. He grinned on his way back to the court cells.

Lynn’s lawyers could apply for him to be released on bail ahead of a fresh trial.

-AAP