Lamarre-Condon, 31, 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 former senior constable'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.
Under cross-examination on Wednesday, ballistics expert Lucas Van Der Walt rejected a theory for how a bullet hole may have ended up on Mr Baird's bedroom door when Mr Davies was killed.
Defence barrister John Stratton SC asked Mr Van Der Walt whether the bullet could have passed through a body before creating the hole in the door.
"That's impossible," the ballistics expert said.
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 stippling would be on the body (in Mr Stratton's suggestion) ... in this case, I've got clear stippling (on the door) that prevents that scenario," Mr Van Der Walt said.
The hole in the bedroom door was only discovered more than two years after the men died and investigators found a gun was fired from the hallway into the bedroom.
Investigators noticed a plastic hook covering an old defect in the bedroom door and, after scraping away some paint and putty, a bullet hole was found, the jury heard.
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 the presence of propellant particles, indicative of stippling.
The observations of the bedroom door are not the first time the 15-member NSW Supreme Court jury has 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 jury also heard that Lamarre-Condon had previously visited the farm in Bungonia where he allegedly tried to sink the bodies of Mr Baird and Mr Davies in a dam.
A statement from Michael Cella, son of the owner of Cella Farm, was read to the court who said he took Lamarre-Condon there on a weekend away in November 2023, three months before the two men died.
The trial continues.
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