Senior constable Beau Lamarre-Condon allegedly said the man who murdered Lilie James was stupid because he got caught on CCTV.
The 31-year-old has pleaded not guilty to the murders of his ex Jesse Baird and their new partner Luke Davies after they were shot dead with his police pistol in February 2024.
The day before the men were shot dead, former officer Ben Higginson says Lamarre-Condon spoke to him about his work on the investigation into the murder of Ms James in 2023.
James was killed by her ex-boyfriend Paul Thijssen in the bathroom of a gym at St Andrew's Cathedral School in central Sydney.
Lamarre-Condon was "blasé" when discussing the actions of the killer, Higginson told a NSW Supreme Court jury on Friday.
"He thought Paul was stupid for doing it on CCTV," Higginson said.
"He asked, 'If he hadn't done it and then committed suicide, would he have got away with it?'"
Higginson said Lamarre-Condon also asked him about how police searched the phones of suspects, including how they connected to phone towers and accessed social media data.
A second former police colleague has also told the jury about a "weird" conversation regarding investigative procedure.
The day after the discussion with Higginson, Lamarre-Condon disguised himself as an UberEats driver and entered his ex's house armed with his police pistol.
Both Baird and Davies were fatally wounded after three shots were fired within a minute.
Lamarre-Condon, who has since left the force, later dumped their bodies south of Sydney and Baird's belongings in a skip bin in Cronulla.
But he argues both men were killed in self-defence in two separate violent struggles and his actions to clean the scene and dispose of the bodies showed his panic.
Jurors on Thursday heard from Alexandra Scobie about Lamarre-Condon's alleged questioning about whether records from a phone could still be obtained if the device was switched off.
In the late January 2024 conversation, he also asked her if hire cars could be tracked, she testified.
Scobie said she received a rushed phone call from her friend later that night, when he tried to reassure her about his questions.
"I'm not gonna do anything illegal," Lamarre-Condon allegedly told her.
He allegedly murdered Baird and Davies on February 19.
The men's bodies were left in surfboard bags in the sharehouse's courtyard overnight.
The second of Baird's housemates is expected to give evidence on Friday after her friend told the jury how she was confused to see the bags leaking a red liquid.
"I thought it was rusted water from the outdoor furniture," the housemate, known by the pseudonym Belinda Smith, said.
The bags were removed by the next morning and the two men's bodies were taken 200km away, covered with sticks and rocks.
The trial continues.
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