The former senior constable, 31, has pleaded not guilty to the February 2024 murders of Mr Baird and his new partner, Luke Davies, saying they were killed in two separate violent struggles.
Nicole Harvell, a former colleague of Lamarre-Condon, told the NSW Supreme Court jury he confided in her about an Instagram story Mr Baird could not see showing a bunch of flowers.
The caption of the image said: "When he's in Melbourne but still sends you these".
Sen Const Harvell said the photo was designed to imply Mr Baird had sent the flowers to the accused, despite the pair not being in a relationship.
But Lamarre-Condon had downloaded the generic photo online.
She said Mr Baird found out about the ruse so Lamarre-Condon enlisted his mother Coleen Lamarre - also a police officer - to cover his tracks.
"He went and purchased flowers to try and lie to Jesse ... (he spent) $160," Sen Const Harvell said.
Lamarre-Condon then sent a different photo to Mr Baird showing his mother with the fresh bouquet.
The bouquet had a handwritten note to imply Ms Lamarre had been the intended recipient and they were sent from her partner, who was in Melbourne, the jury heard.
"(Lamarre-Condon) told me his mother wrote the note ... so it wouldn't be (his) handwriting," Sen Const Harvell said.
Ms Lamarre's hiring of a car, allegedly for her son, the day before the alleged murders also featured in the trial on Tuesday.
CCTV from February 18 shows the former police officer's mother hiring an SUV while her son waits outside.
Lamarre-Condon got his mother to hire the Mazda CX-5 because he intended to only kill Mr Baird, Mr Hatfield previously told the jury.
But after being surprised by Mr Davies making a triple-zero call, he shot the 29-year-old through a door and had to upsize his vehicle and make more purchases to accommodate the extra body, the prosecution alleges.
Ms Lamarre has not been charged over the alleged murders.
Muffled audio of the triple-zero call made from Mr Davies' phone was played to the jury.
An operator can be heard saying, "Caller disconnected, no request".
"I heard a male say, 'eff off', call dropped out," she says.
Lamarre-Condon's barrister says his client made the call after killing Mr Baird in self-defence but it was cut short by a second struggle in which Mr Davies died.
CCTV played for the jury on Tuesday shows Lamarre-Condon arriving on foot at a different car rental depot about 9pm on February 19, 2024, 12 hours after the killings.
The accused can be seen driving out of the depot in a Toyota Hiace van, which was later discovered to have significant blood staining by forensic officers.
GPS data from the van shows it was parked near the rear roller door of Mr Baird's house in Paddington about 11pm, prosecutor Brett Hatfield SC said.
It left 22 minutes later, he said.
Further footage of the van near Mr Baird's house after midnight on February 20 would be played later in the trial, the prosecutor said.
The men's bodies were left in surfboard bags in the sharehouse's courtyard overnight.
Mr Baird's housemates took a photo of red liquid leaking from the bag when they discovered it later that day.
The purchase of the second surfboard bag after the deaths is a further indicator of the former officer adapting to the unexpected killing of Mr Davies, the prosecution alleges.
But Lamarre-Condon's barrister says the lengths he went to in cleaning and disposing of the bodies showed his panic, rather than a murderous intent.
The trial continues.
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