Moore is accused of killing four men in a 75-day period during 2010. He has pleaded not guilty to four counts of first-degree murder.
Two of the men killed were 18-year-old Courthney Facey and 23-year-old Mike James.
Inside court on Thursday, Shirlon Marshall testified that he was good friends with both Facey and James.
Marshall said that James had mentored him as a chef.
On Sept. 29, 2010, Marshall was at home when he said he got a call from James, who was parked nearby, in the Weston Road and Lawrence Avenue West area.
Marshall went downstairs, where he saw James sitting on the back of a car.
Facey was inside the car, Marshall told the court.
Marshall told his friends he was going to get some cigarettes and would be back.
He told the court that he had been gone for about a minute when he heard gunshots.
Marshall said he saw a black, four-door BMW turning out of the alleyway where his friends were parked. Both men had been shot.
A paramedic testified earlier Thursday that Facey died en route to hospital.
James was shot in the stomach. He died in hospital.
Earlier in the month of September 2010, a 27-year-old man named Jahmeel Spence was shot and killed in Scarborough.
In November 2010, 45-year-old Carl Cole was killed.
The Crown contends that all four men were shot with the same gun.
The trial continues.