A couple found guilty of shooting their former son-in-law in a premeditated murder in the driveway of his home claim an unknown person could have been the culprit.
Noelene June Jordan and Cedric Harper Jordan, both in their 70s, were sentenced to 22 years' jail in 2023 for murdering 36-year-old Shane Barker in 2009.
The married pair was motivated by ill-feelings towards Mr Barker, who they believe was abusive towards their daughter and granddaughter.
Mr Barker, who lived in Campbell Town in Tasmania, was shot four times at night with sub-sonic bullets fired from a .22 calibre firearm fitted with a silencer.
A judge ruled the couple travelled from their home with common intent and Mr Jordan, who had a lifetime of gun experience, fired the shots.
The Jordans have appealed their conviction on several grounds, including that the jury's guilty verdict was unsatisfactory.
They claim an alternative theory in the circumstantial case, in which the murder weapon has never been found, wasn't considered.
The same type of cartridge found at the scene of the murder was also discovered at the Jordan's holiday shack.
Mrs Jordan's lawyer Fran McCracken told Tasmania's Court of Criminal Appeal Mr Barker may have once used the gun involved in his murder at the shack.
Ms McCracken said the unregistered gun may have then changed hands and was used by a "third party" to kill Mr Barker.
"Is it not asserted there is a particular offender or offenders pointed to by the Jordans," she said on Monday.
"Merely the circumstances ... they were both saying 'we don't know who it was but it was not me'."
Crown prosecutor Daryl Coates said it was "fanciful" to suggest somebody else killed Mr Barker.
He said the Jordans had a very strong motive for murder, lied about their whereabouts and were placed in the area by phone data around the time of the killing.
There was also evidence at the trial the Jordans had access to a .22 unregistered rifle and Mr Jordan had said it would be a "good rifle to kill people with", Mr Coates said.
Mr Coates said ammunition found at the scene was the same as some found at the Jordans.
"The jury were properly satisfied beyond reasonable doubt that they committed this crime," he said.
The Jordans are also appealing on the grounds a "demonstration" at the trial was prejudicial and a relationship between a juror and a reserve juror may have impacted deliberations.
Mr Barker and the Jordans' daughter Rachel had separated two-and-a-half years before the murder.
Sentencing Justice Robert Pearce said Mr and Mrs Jordan were highly protective of Rachel and their granddaughter and perceived Mr Barker had behaved "very badly".
Justice Pearce said abuse claims were "improbable" but it wasn't an issue for the trial to decide.
A decision on the appeal will be made at a later date.
