Disgraced former police detective and convicted murderer Roger Rogerson should be re-tried because fresh evidence has emerged about the possible murder weapon, an appeal court has heard.
Rogerson, 79, and fellow former detective Glen McNamara, 60, were jailed for life in 2016 for the cold-blooded execution of drug dealer Jamie Gao in a south Sydney storage locker in May 2014.
They also were convicted for robbing the 20-year-old student of nearly three kilograms of methamphetamine.
The NSW Court of Criminal Appeal, which is this week hearing the pair's separate conviction and sentence appeals, has been told a witness came forward in October 2016 about passing a small-calibre handgun to McNamara before the murder.
The .25-calibre Baby Browning semi-automatic pistol was the same type as those McNamara had been searching for online before the murder and was in a relatively small class of weapons capable of firing the bullets that killed Mr Gao, Rogerson's barrister said on Tuesday.
The witness, known as Witness A, also testified on Monday that during the pistol handover at the Picton Hotel in early 2014, McNamara acted as though he'd "won the lotto" and then said "don't tell Roger".
"That goes to the whole issue of whether the appellant Rogerson had any knowledge of a gun being involved and any knowledge of a robbery, let alone a murder," barrister John Stratton SC said on Tuesday.
Witness A said he'd not realised the significance of the exchange, even after reading news of the murder.
Mr Stratton painted him as a "very credible" witness who'd made no attempt to conceal his mistakes and former crimes.
Justice Andrew Bell, the state's second-highest-ranking judge, however pointed out the woman who'd possessed the gun earlier had contradicted Witness A's evidence about him collecting it from her doorstep.
"It still strikes me as quite a striking inconsistency," the Court of Appeal president said.
Rogerson is also contending the jury's verdict was unreasonable and couldn't be supported by the evidence.
Unlike McNamara, Rogerson hadn't met Gao before the day of the murder and arrived at the storage locker driving a car registered under his name.
The older former detective didn't wear sunglasses, a cap or a hoodie but McNamara had - "knowing there is going to be a killing", Mr Stratton reasoned.
"Everything about the conduct is consistent with him (Rogerson) not knowing what is going on," he said.
Parking his mobility walker behind him, Rogerson has followed the hearing via audiovisual link from a small room in prison.
Representatives of McNamara, who is also following via AVL from prison, are expected to begin oral submissions on Wednesday.
The pair were found guilty in June 2016 after a four-month trial that heard Mr Gao was lured to a darkened storage shed in Padstow and shot dead, before Rogerson and McNamara attempted to cover their tracks by dumping his body at sea.
They used the skills and knowledge honed over their years as sworn NSW police officers to gain Mr Gao's trust, the sentencing judge found.
Although gunshot residue found on Rogerson's clothing pointed to the possibility he was the triggerman, the judge said he couldn't be sure who fired the fatal shots.
At the time of the murder, both men had left the force long ago, with McNamara switching to writing true crime books and working as a private detective.