Beau Lamarre-Condon's offer to admit to the manslaughter of his ex-partner, Jesse Baird, was rejected by prosecutors at the start of his trial in the NSW Supreme Court on Monday.
The 31-year-old senior constable pleaded not guilty to murdering Mr Baird and his new partner, Luke Davies, in the former's home in Paddington, in Sydney's eastern suburbs.
The crown prosecutor gave a brief outline of the case against Lamarre-Condon during the empanelment of the 15-member jury for the trial estimated to last 12 weeks.
Lamarre-Condon was romantically involved with Mr Baird for a few months in 2022 and 2023 but his behaviour became concerning after they split up, Brett Hatfield SC said.
"(Lamarre-Condon) developed an infatuation and obsession with Jesse Baird, which manifested itself in a range of compulsive behaviours," Mr Hatfield told jurors.
After the pair split up, Mr Baird allegedly stopped all contact with Lamarre-Condon.
The officer then stalked his ex, damaged his car and broke into his house, the prosecutor told the jury.
By early 2024, the senior constable allegedly began planning the murder of his ex by investigating how to conceal the sound of gunfire, buying a surfboard cover to hide the bodies and retaining his police pistol.
Prosecutors allege Lamarre-Condon entered Mr Baird's home on February 19 disguised as an Uber Eats delivery rider wearing a motorcycle helmet.
He is accused of shooting Mr Baird twice in his kitchen before moving to a bedroom and killing Mr Davies.
Over the next few days, the senior constable allegedly moved the bodies to a rural property and disposed of them, after unsuccessfully trying to sink them in a dam, Mr Hatfield said.
Lamarre-Condon has also pleaded not guilty to breaking into the Paddington house about six months before the killings and stealing Mr Baird's phone and wallet.
More than 100 witnesses are expected to be called during the trial including dozens of police officers and friends and family of the three men.
Witnesses from near the area where the bodies were found are also due to testify.
Lamarre-Condon, who appeared in court wearing a light-coloured suit jacket and dark tie, is allowed access to a laptop during the trial.
While the computer cannot access the internet, he can use it to give instructions to his lawyers and access electronic versions of the brief of evidence, Justice Natalie Adams said.
The mammoth trial is expected to last at least 12 weeks given the number of witnesses to be called.
"I'm going to do everything in my power to ensure this trial is completed by Christmas," Justice Adams said.
Mr Hatfield is expected to begin his opening address to the jury on Monday afternoon.
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