Marks caused by a gun at close range were found on the bedroom door through which Luke Davies was allegedly shot and killed, a jury has heard.
Former police officer Beau Lamarre-Condon has pleaded not guilty to the murders of Mr Davies and his new boyfriend Jesse Baird, saying both men were killed in self-defence.
The 31-year-old's barrister has suggested Mr Davies was killed in a violent struggle after picking up the officer's discarded gun after the killing of Mr Baird.
But prosecutors say Mr Davies, 29, was murdered through a bedroom door when Lamarre-Condon heard him trying to make a triple zero call.
Ballistics expert Lucas Van Der Walt told the court on Wednesday an examination of the bedroom door more than two years after the men died provided evidence a gun was fired through the door.
Investigators noticed a plastic hook was covering an old defect in the bedroom door and, after scraping away some paint and putty, a bullet hole was found, the jury heard.
Around the hole, stippling was identified, which occurs when gunpowder particles by a fired gun cause a cone pattern on a surface, Mr Van Der Walt said.
The ballistics expert said stippling from a gun of similar calibre to the police pistol would only be noticeable at a range between one and 60 centimetres.
The particles would be travelling at a speed of 350 metres per second, he said.
"Fine grains ... impacting at that speed with a soft surface such as paint ... is going to pepper itself into that softer surface," Mr Van Der Walt said.
"As the layers (of paint and putty) are being removed, it reveals more areas of propellant impact or stippling."
A video of a test firing into Mr Baird's bedroom door at Sydney Police Centre and a comparison of the test hole and original hole showed similar stippling marks around the two bullet holes.
Mr Van Der Walt said a chemical test of the door confirmed propellant particles indicative of stippling were present.
The observations of the bedroom door are not the first time the 15-member NSW Supreme Court jury have been asked to consider the effect of stippling.
A crime scene officer previously said he observed the phenomenon around the bullet wound sustained by Jesse Baird, which the prosecution alleges was committed "execution-style".
The photographs of those marks were only shown to the jury and not the public gallery.
But a forensic pathologist said the stippling was not visible when she conducted the autopsy on Mr Baird two days after his body was found.
Lamarre-Condon's barrister says Mr Baird was killed in a violent struggle after which Lamarre-Condon's police pistol was flung across the room.
The trial continues.
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