Bulger then shot McIntyre, he said.
Kelly also described how Bulger allegedly strangled two 26-year-old women: Debra Davis, Flemmi's girlfriend, and Deborah Hussey, daughter of Flemmi's common-law wife.
Flemmi has testified previously that he watched Bulger kill both women. Weeks testified that he was also present when Bulger killed Hussey.
Bulger, Kelly said, was a "hands-on killer who was the leader of an extensive criminal enterprise."
Bulger's lawyer, however, said Flemmi is the one who killed the women and decided to pin the murders on Bulger after Bulger fled Boston in 1994.
Carney said Bulger had no motive to kill Davis or Hussey, who were close to Flemmi, but not Bulger.
Carney insisted that Bulger was not an FBI informant but instead paid FBI agents to tip him off when he and his gang were being investigated or about to be indicted.
"James Bulger never, ever — the evidence will show — was an informant," Carney said.
Carney said it went against Bulger's Irish heritage to be an informant. He also said Bulger was not close enough to members of the local Mafia to provide any useful information to authorities.
Carney said former FBI agent John Connolly — who was convicted of racketeering for tipping Bulger and Flemmi to an indictment — fabricated a lengthy FBI informant file for Bulger to cover up the fact that he was regularly seen meeting with Bulger.
Kelly said Bulger's gang succeeded by instilling fear in other criminals and corrupting Connolly and other law enforcement officials.
"It was part of a strategy they had, and it worked for them," Kelly said.
Kelly slowly read the names of each of the 19 victims while showing their pictures to the jury.
The first prosecution witness, retired state police Lt. Robert Long, identified surveillance video and photos of Bulger taken during a 1980 investigation. The video showed Bulger meeting with various organized crime figures at an auto repair garage in Boston's North End.
Testimony was set to resume Thursday.