The former police officer has pleaded not guilty to murdering his ex partner Jesse Baird and Luke Davies in 2024.
The bodies of the men, aged in their 20s, were found at a rural property inside surfboard bags.
One friend, known by pseudonym Fiona Rosso, became highly emotional giving evidence at the former officer's NSW Supreme Court trial on Wednesday.
She described drinking champagne and unpacking groceries when Lamarre-Condon unexpectedly turned up at her house days after the incident.
"He started crying and he said words like 'I'm saying goodbye, I've come to say goodbye'," she told the jury.
He then explained he had "done something bad" and asked whether she had seen the news.
At the time, police had publicly announced they were looking into the disappearance of Mr Baird and Mr Davies.
Lamarre-Condon then asked her to search the definition of schizophrenia online, telling her he had had an out-of-body experience and could not control his actions, the woman said.
Her voice cracking and hands shaking, she recounted later sitting on the footpath in shock with another glass of champagne as he scrubbed the back of his white van.
"I didn't look into the van at all," she told the jury.Â
"I just remember sitting there thinking, 'What the f***.'"
A statement by a neighbour read out in court described how the 68-year-old had wandered out onto the street after hearing dogs barking.
She found Ms Rosso sitting on the roadside and a man she did not know moving in and out of the van.
With Ms Rosso appearing to act normally, the neighbour went back to bed.
The following day, the van was gone but a police vehicle was sitting in its place.
Lamarre-Condon claims he killed the men in self-defence after entering their terrace to retrieve his belongings.
His offer to plead guilty to Mr Baird's manslaughter was rejected by prosecutors.
Ms Rosso said she tried to keep things calm and normal while Lamarre-Condon was at her home out of fear he would react or retaliate against her.
She told the jury he described driving two-and-a-half hours with another female friend - known to jurors as Elizabeth Kennedy - to dispose of the bodies in a dam.
Crown prosecutors on Tuesday read a police statement in which Lamarre-Condon claimed Ms Kennedy lied about her involvement in trying to hide the bodies.
He wrote that his friend urged him not to go to the police as they would not believe him.
"This is like Taylor Swift's song 'no body, no crime'," she allegedly said.
"We have to get rid of them straight away."
Ms Rosso on Wednesday testified her friend also mentioned an occasion when he had shown Mr Baird his police firearm at the now-deceased man's Sydney home.
Mr Baird accidentally let off a round and the hole had to be patched up, Ms Rosso said she was told.
"I was like, 'Oh my god, you're basically telling me that you've killed Jesse,'" she said.
She also testified Lamarre-Condon's mother had texted him the code word "hot chocolate", meaning police had searched her home after the alleged murders.
She recalled a visit by the former youth command officer about a week before the incident to go over lines for an acting class at her home.
He went off script, asking if she would help bury a body for him, she said.
But she did not interpret the question as literal.
The Crown alleges Lamarre-Condon killed Mr Baird "execution-style" at close range through a plan borne of a jealous obsession, before shooting Mr Davies to eliminate a witness.
The trial continues on Thursday.
Lifeline 13 11 14
beyondblue 1300 22 4636
27°C