A 19-year saga over the murders of an Australian couple could finally come to an end today, when the NSW Court of Criminal Appeal reveals whether their son Jeffrey Gilham will be acquitted of the crime or face a second re-trial.

In the early hours of August 28, 1993, Helen Gilham, 55, and her 58-year-old husband Stephen Gilham were were repeatedly stabbed in their southern Sydney home and then set alight .

Their eldest son Christopher Gilham was also stabbed to death on the same morning.

The only surviving member of the family, Jeffrey Gilham, admitted to killing his brother Christopher, but said he did so in a fit of rage after discovering that his older sibling had killed their parents.

Police initially accepted Gilham's story, allowing him to plead guilty to manslaughter for killing his 25-year-old brother.

But there were others who did not accept it, most notably Jeffrey Gilham's uncle Tony Gilham, who was convinced that his nephew was guilty and began campaigning for him to be brought to trial

Police eventually re-opened the investigation and in 2000 a coroner recommended that Gilham be charged with the murder of his parents.

Eight years later, after one trial in which the jury failed to reach a verdict, Gilham was convicted over the murder of his parents and given two consecutive life sentences.

The sentencing judge, Justice Roderick Howie, described him as "a consummate liar and a brilliant actor" whose offences were "truly heinous" [link to judgment].

But the case was far from over.

Gilham appealed against the convictions to the state's highest court and presented new expert scientific evidence that cast doubt over a key part of the prosecution case against him.

An American toxicologist, David Penney, told the court that - contrary to the Crown case - Stephen, Helen and Christopher Gilham must have been alive when the fire was lit because they had significant amounts of carbon monoxide in their bloodstream.

This undermined the Crown's argument - based on testimony from its own expert - that Christopher Gilham had a "negative" level of CO in his bloodstream and thus must have been dead before the fire was lit.

It also brought into question the timing and sequence of events presented to the jury by Crown Prosecutor, Margaret Cunneen, SC, including the claim that there was a 20-minute gap between the stabbings and Gilham's arrival at his neighbour's front door.

Professor Penney's evidence was not accepted by Tony Gilham.

Earlier this year, he released a report into carbon monoxide levels by one of the other forensic pathologists who gave evidence in Gilham's trial, Dr Allan Cala, which contradicted Penney's claims.

But this report was not part of the evidence given to the three-judge appeal panel of Justice Peter McClellan, Justice Elizabeth Fullerton and Justice Peter Garling.

They were highly scathing of the Crown case on the issue of CO, with Justice Garling asking whether it was "now right to say that the facts are closer to the appellant's case than what the Crown put to the trial?".

On December 2 last year, they quashed Gilham's conviction for the murder of his parents and released him on bail after three years spent in Goulburn jail.

Today the panel will hand down its final decision on whether the 42-year-old is to be acquitted of all charges or forced to face a second re-trial.

An acquittal decision would mark the end of a 19-year-long saga that has involved nearly a dozen court cases and coronial hearings occupying hundreds of hours, thousands of newspaper column inches and an extraordinary emotional rollercoaster for the members of the extended Gilham family and their friends.

Coming just four months after Gordon Wood was acquitted over the murder of his Girlfriend Caroline Byrne, it would also raise further questions about the way alleged offenders are tried in NSW.

In particular, it would raise questions about the use of forensic scientific evidence to prove a person's guilt or innocence, and the ability of juries to understand this evidence and its fallibility.

- Sydney Morning Herald