The bag - containing his body - vanished later that night, a jury has heard.
Former police officer Beau Lamarre-Condon has pleaded not guilty to the murders of his ex Mr Baird, 26, and Luke Davies, 29, saying the men died from gunshot wounds during two separate violent struggles.
The senior constable entered Mr Baird's Sydney terrace in February 2024 armed with his police pistol and heavily disguised.
After the two men died in the terrace on February 19, Lamarre-Condon attempted to clean the scene and left their bodies in surfboard bags in the Paddington home's courtyard through the afternoon and evening.
He moved them late that night, the NSW Supreme Court jury has heard.
Mr Baird was due to move into a new house the day after he died.
He was later reported missing and a detective on Monday recalled how Mr Baird's housemates on February 21 spoke about their confusion at the sight of the two surfboard bags.
The housemates are known under pseudonyms in the proceedings.
"They're not mine and they're not Belinda's," housemate Sarah King told Detective Senior Constable Alistair Wright.
"(Jesse's) never had surfboards here and he's never spoken about surfing."
The confusion grew once the two women noticed a pool of red liquid they initially thought to be rust leaking from the bags.
"I don't know if this has anything to do with it," Ms King told the detective before showing him a photograph of the liquid.
"I don't know if I'm overreacting."
Det Sen Const Wright will undergo cross-examination on Tuesday when the weeks-long trial resumes.
Lamarre-Condon allegedly dumped the two men's bodies at a rural Greek monastery after unsuccessfully trying to sink them in a dam south of Sydney.
He later handed himself into police.
The jury has heard evidence from multiple witnesses about Lamarre-Condon's jealousy in the months leading up to the alleged murders.
A former colleague said the senior constable told her how he would go into Mr Baird's phone and tamper with his social media and contacts.
"I thought 'that's pretty f***ing crazy'," Kate McKinley said.
"He was jealous and he was annoyed and pissed off."
The trial continues on Tuesday.
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