Former senior constable Beau Lamarre-Condon, 31, is contesting two murder charges relating to his ex, TV presenter and AFL goal umpire Jesse Baird, 26, and Luke Davies, 29.
His barrister has told his NSW Supreme Court trial the two men were killed in self-defence, saying Mr Baird was killed in a violent struggle after which Lamarre-Condon's police pistol was flung across the room.
Mr Davies then picked up the pistol and a second struggle with the police officer ended in the 29-year-old pulling the trigger, accidentally killing himself, according to the defence case.
But the forensic pathologist who conducted autopsies on the pair told the jury Mr Baird would not have been able to make a meaningful effort to throw the gun after being shot.
Kendall Bailey said her post-mortem examination found Mr Baird sustained two bullet wounds, including one travelling through significant portions of his brain and central nervous system.
"Someone shot through that area of the brain ... wouldn't be able to fling a gun across the room?" prosecutor Brett Hatfield SC asked the pathologist.
"It would be instantly incapacitating," Dr Bailey said.
"I don't think that person is making any conscious movements."
A crime scene officer was earlier questioned about how DNA, which could not be tested, got into the barrel of the alleged murderer's police pistol.
Greg Moon concluded evidence on Tuesday and disagreed with Lamarre-Condon's barrister about the likelihood of DNA being able to travel through a hole in a door.
"The possibility of biological material finding its way from a wound to the deceased through a hole in the door ... and into the barrel of a gun - the likelihood of that approaches zero," defence barrister John Stratton SC suggested.
"I disagree ... I believe it can still happen," Mr Moon said.
"I'm putting to you it's very improbable," Mr Stratton said.
"I disagree," Mr Moon replied.
Mr Moon said biological material would not be found in the barrel of a gun if it was fired again, due to the high heat killing any DNA.
The bullet hole allegedly caused by the shot that killed Mr Davies was only found in July, more than two years after the men died, the jury of 15 has been told.
The hole was less than one centimetre in diameter.
Lamarre-Condon, 31, accepts he shot Mr Baird, who'd months earlier called time on a brief, second relationship.
But he argues he acted in self-defence after entering the home in disguise in February 2024 to retrieve personal items.
The Crown argues Lamarre-Condon murdered Mr Baird out of jealousy and then eliminated the witness, Mr Davies, as the 29-year-old tried to make a triple zero call.
Mr Moon also gave evidence about the phenomenon of stippling, where gunpowder particles ejected when a gun is fired cause a cone pattern on a surface depending on the distance from the firearm to the surface.
On cross-examination, Mr Moon said the only wound he saw with stippling was the gunshot wound to Mr Baird's right temple.
Dr Bailey said she did not observe stippling on any of the gunshot wounds but the condition of the bodies had been affected by decomposition.
Both parties agree Mr Baird was killed first with two gunshot wounds before Mr Davies was killed with a third shot.
The former officer has pleaded not guilty to both murders.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
Men's Referral Service 1300 766 491
8°C