The 31-year-old has pleaded not guilty to murdering Jesse Baird and Luke Davies with his police-issue pistol at their inner-city Sydney terrace in February 2024.
He stepped into the witness box for a third day of questioning in the NSW Supreme Court on Tuesday, quizzed about his relationship with Mr Baird.
The pair dated from December 2022 until April 2023, when they broke up over Instagram messages the TV presenter sent to another man he was also dating.
Jurors previously heard at some point after this break-up, Lamarre-Condon had gone into Mr Baird's home without his knowledge and taken his mobile phone.
He then allegedly blocked contacts, turned off alarms, deleted photos of the TV presenter with other men and changed his Snapchat settings to reveal his location.
The 31-year-old on Tuesday said these claims were a lie.
Crown prosecutor Brett Hatfield SC took the former police officer to a number of occasions where he bumped into Mr Baird without planning.
On one occasion at the Royal Hotel in Paddington, Lamarre-Condon allegedly used his authority as a police officer to view CCTV footage of Mr Baird drinking there with another man.
He denies this, saying he was invited to the hotel and only saw the CCTV footage while helping police investigate an alleged shoulder bump unconnected to Mr Baird.
The 31-year-old also ran into his love interest at a nightclub on his birthday and while out shopping with a friend.
"You had put his Snapchat maps on and you were able to follow him that way?" Mr Hatfield asked.
"No," Lamarre-Condon replied.
After encountering Mr Baird while out shopping, the former senior constable texted a friend to let her know.
"Was it sus at all or did you make it look like a complete coincidence?" she texted.
"Not sus at all," he replied.
Lamarre-Condon also fired back at prosecutors after being accused of stalking Mr Baird by saving his social media photos after they had broken up in April 2023.
"If you're going to accuse me of stalking, you're going to have to show my phone records," Lamarre-Condon shot back at the Mr Hatfield.
He admitted looking at Mr Baird's posts online but denied this was stalking.
Mr Hatfield earlier asked about the initial months of Lamarre-Condon's relationship with Mr Baird between December 2022 to February 2023.
Lamarre-Condon denied being obsessed with the other man.
"Smitten yes, obsessed no," he said.
He admitted to going through Mr Baird's phone during a farmstay vacation in March 2023 and unfollowing two to three people.
Lamarre-Condon accepted it was a breach of trust and privacy, but said Mr Baird had exaggerated the number of people he unfollowed when discussing the incident with a friend.
"Everyone adds their own salt and pepper," he told the court.
Lamarre-Condon posted an edited video of the farmstay trip on Instagram.
He denied the clip was designed to give a false impression about the status of the pair's relationship at the time.
Mr Baird and Mr Davies were fatally shot in their Paddington home on February 19, 2024.
Prosecutors allege Lamarre-Condon was obsessed with Mr Baird despite the couple breaking up, staking out the other man's house for hours before entering the home to assassinate him.
The 31-year-old claims he disguised himself as an Uber Eats driver to retrieve his belongings from Mr Baird's home and has argued self-defence for the killings.
He says he accidentally shot Mr Baird during a tussle in the kitchen and Mr Davies shot himself during a separate altercation as he tried to leave the home to flag down an ambulance.
He led police to where their bodies were stuffed in surfboard bags and buried behind a rural monastery when he handed himself in days after the incident.
Lamarre-Condon will continue giving evidence on Wednesday.
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