They said the McMichaels wanted to detain and question Mr Arbery as he had been seen running from a nearby home under construction.
Travis McMichael, the only one of the three defendants to take the witness stand, testified that he shot Mr Arbery while protecting himself.
He claimed Mr Arbery turned and attacked with his fists while running past the parked truck.
Prosecutors said there was no evidence Mr Arbery had committed any crimes in the defendants’ neighbourhood.
The former high school American football player had enrolled at a technical college and was preparing to study to become an electrician like his uncles.
Meanwhile, the defence cited a Georgia law that allows anyone to make a citizen’s arrest when they have a reasonable suspicion someone is fleeing a serious crime.
That law has been repealed in the wake of Mr Arbery’s death.
Mr Arbery, a keen jogger, had not stolen anything on his frequent runs through the Satilla Shores neighbourhood, the court heard. When he died there was nothing in his pockets, not even a phone or wallet.
Security footage emerged of him entering the home under construction on the day he was killed.
But it showed he had taken nothing and had either stopped to drink from a tap, or to examine wiring which was interesting to him as a would-be electrician.
Authorities in Brunswick were accused of turning a blind eye to the case as the white gunmen were only arrested two-and-a-half months after the killing when the shocking mobile phone footage emerged.
“Ahmaud Arbery’s killing – witnessed by the world on video – is a devastating reminder of how far we have to go in the fight for racial justice in this country,” President Joe Biden said in a statement.
“Mr Arbery should be here today, celebrating the holidays with his mother, Wanda Cooper Jones, and his father, Marcus Arbery. Nothing can bring Mr Arbery back to his family and to his community, but the verdict ensures that those who committed this horrible crime will be punished.”
Kamala Harris, the vice president, criticised the defence for trying to “dehumanise” Mr Arbery. In a statement Ms Harris, a former prosecutor, said they “chose to set a tone that cast the attendance of ministers at the trial as intimidation, and dehumanised a young black man with racist tropes”.