A TOOWOOMBA man convicted of brutally murdering his grandfather wants his conviction overturned because his lawyers say key witnesses at his trial were unreliable.
Corey James Lovell and his mother Samantha Ann Brownlow, both of Toowoomba, have been imprisoned for life for murdering Bundaberg man Robin Behrendorff in his house in 2011.
Mr Behrendorff was Brownlow's stepfather and Lovell's grandfather and in 2013 the pair were convicted of bludgeoning and stabbing him to death at his Burnett Heads home.
Lovell has appealed this conviction at Queensland's highest court.
On Thursday, his barrister Tim Ryan argued that the judge at Lovell's trial did not properly warn the jury to consider that one of the main prosecution witnesses was unreliable.
He also raised concerns the jury deliberated for less than an hour before returning the guilty verdict.
At the trial, a 15-year-old girl, who was Lovell's sister and Brownlow's daughter, gave evidence saying Lovell told her that he had punched and kicked his grandfather until he did not breathe.
But Mr Ryan said the witness had admitted she lied to police and that the judge should have warned the jury to consider her unreliable.
"She admitted in her evidence that she had lied to police," Mr Ryan said.
"The reason she said she told that series of lies to police was because she was asked to do so by her mother.
"The general concern that I express is that … she minimised the involvement of her mother and at the same time overstated the involvement of (Lovell)."
But barrister Greg Cummings, representing the Crown, said evidence suggested otherwise.
He said if she was going to over exaggerate anyone's involvement it would be her mother's because her mother had threatened her several times, including a threat that she would slit her daughter's throat.
Evidence showed the witness was initially pressured into helping her mother kill Mr Behrendorff, the court heard.
Mr Cummings also argued that if the judge had warned the jury that the witness was unreliable, it would have "completely destroyed" the defence case and evidence they got from her during cross examination.
The court heard Lovell's defence lawyers during his trial did not ask the judge to direct the jury about the witness being possibly unreliable.
The Queensland Court of Appeal has reserved its decision. - ARM NEWSDESK