BOSTON — The former right-hand man of James “Whitey” Bulger testified Monday that he saw the alleged mobster open fire on a car and kill two men in 1982.

Kevin Weeks took the witness stand at Bulger’s racketeering trial and said he saw Bulger extort multiple businessmen and drug dealers for a cut of their profits.

Weeks said he first developed a friendship with Bulger in the 1970s while he was working as a bouncer at Triple O’s, a South Boston bar where Bulger did business as the leader of the Winter Hill Gang. Soon, he said, he was working as an enforcer, driving around South Boston and picking up cash from local bookmakers Bulger and his gang were extorting.

In May 1982, Weeks said, he went from being muscle to helping Bulger in a murder.

The target was Edward “Brian” Halloran, a man who Bulger had heard was cooperating with authorities.

Weeks said that after another Winter Hill member told Bulger he had spotted Halloran on a pay phone, Bulger drove to one of the gang’s hangouts in a “hit car.” Bulger was wearing a wig and fake moustache, he said.

Bulger told him to drive to the waterfront and wait there, Weeks said. A short while later, Bulger drove up, with a man wearing a ski mask lying in the back seat.

Weeks said Bulger handed him a two-way radio, told him to watch Halloran in a restaurant, then let him know when Halloran was coming out.

Weeks said he told Bulger, “The balloon’s rising,” as Halloran started to leave the restaurant, a reference to Halloran’s nickname, “Balloonhead.” When Halloran walked outside, Weeks said he told Bulger, “The balloon’s in the air.”

Halloran got into a blue Datsun driven by a friend, Michael Donahue.

Weeks said he saw Bulger pull up to the car.

“He slid across the front seat and he yelled out, ‘Brian!’ and he proceeded to start shooting,” Weeks said.

The car Halloran and Donahue were in drifted across the road and hit something, Weeks said.

Halloran then got out of the car, and “Jim Bulger just started shooting right at him,” Weeks said. “His body was bouncing on the ground.”

Both Bulger and the person in the back seat fired at the car, Weeks said.