The reaction of the accused, Alan William Delaney, came after he allegedly threatened to kill before the assault.

Mr Delaney has pleaded not guilty to murder, alleged to have happened under Queens Bridge on Boxing Day 2019, and is facing a NSW Supreme Court trial in Queanbeyan that began earlier this week.

Crown prosecutor Nerissa Keay said the physical altercation was the result of Mr Delaney seeking the deceased, Aaron Baxter, whom he accused of stealing his money and meddling in his personal relationship.

Ms Keay said that during the assault, Mr Delaney accused Mr Baxter of telling lies, including "you told my missus you were taking me to the brothel".

The accused, 53, left the scene only when a witness, who was living under the bridge and knew Mr Baxter, told him people across the river were witnessing the incident.

Mr Baxter was taken to Queanbeyan District Hospital but died about two hours later after going into cardiac arrest.

On Thursday, the recorded police interview with Mr Delaney, of Queanbeyan, in the early hours of December 27, 2019, was played to the court.

When an officer told him Mr Baxter had died, he became inconsolable and held his hands to his face.

"Please tell me that's not right ... please," he said.

"This is a dream. Please tell me this is a bad dream.

"I didn't want to do that. It doesn't matter, it's my fault now."

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Earlier in the interview, the accused said he hit Mr Baxter eight to 12 times despite saying he wanted to just "smack him around the mouth to teach him a lesson for interfering and stealing off me".

He accused Mr Baxter of "making things up" and "destroying my whole world because I fell in love with this girl".

The court heard that after the assault, Mr Delaney continued to yell at Mr Baxter from afar.

He then bought cigarettes and wine on his way home.

An autopsy showed Mr Baxter died from internal bleeding within his abdominal cavity, originating from a ruptured spleen.

Mr Delaney had been drinking on Christmas Day with another friend prior to the incident.

He also sent his partner a series of text messages and published Facebook posts, including "now I'm going to snap" and "I've been used for the last time".

In her closing statement, Ms Keay said the evidence established that Mr Delaney's intention was to kill or cause serious harm and that his assault caused the death.

"No doubt, Mr Delaney was very angry with the deceased when he assaulted him," Ms Keay said.

"It's important to look at what he said, what he did and what he said after.

"The last message before the assault was particularly telling: 'now I'm going to snap'. That's exactly what he did."

Ms Keay told the jury that following the assault, in which Mr Delaney injured one of his hands because he "hit the deceased so hard", he posted a photo of his injury and the phrase "one c--- down" on social media.

The trial heard evidence that Mr Baxter had sustained a fall unrelated to the assault and the examination of whether that fall contributed to his fatal injury.

However, Ms Keay said the deceased was "a man whose health deteriorated from the time of the assault".

She said the jury should reject the notion that that fall caused Mr Baxter's fatal injury because of numerous reasons, including an unimpressive witness and that such a fall did not explain the bruises on the deceased.

Ms Keay said that while Mr Delaney's reaction to the news of his friend's death was genuine, the jury may also think "he was in part concerned about himself".

"[He] kept talking about how the deceased had done him wrong. He minimised the violence he perpetrated on the deceased," she said.

Defence lawyer Duncan Berents made brief submissions, including the reasonable possibility that the blunt force trauma was from a source other than the accused, on Thursday afternoon but has reserved his full closing for Friday.

Justice Desmond Fagan will sum up the case before deliberations among jurors, who have also received legal directions about manslaughter if they find murder is not proven.

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