BOSTON — It all depends how you look at it, really.

One man’s hit man is another’s humanitarian.

Johnny “The Executioner” Martorano, who turned government witness and copped to killing 20 men and women as part of Whitey Bulger’s Winter Hill Gang, explained to Whitey’s lawyer Tuesday in federal court here that he was motivated by love of family and friends.

“I didn’t enjoy killing anybody,” he said. “I enjoyed helping a friend if I could.”If anybody insulted, implicated or roughed up his brother or a friend’s brother, if anybody looked at him funny while he was with a date, if anybody ratted on his fellow gang members, if anybody could eyewitness a crime committed by an “associate,” he grabbed a .38 or a knife, a fake beard, a walkie-talkie or a towel to keep the blood off his car, and sprang into action. And somebody usually ended up in a trunk somewhere, sometimes still groaning.

“Family and friends come first,” said the bulldog-faced enforcer, looking natty with slicked back, suspiciously black hair, a dark suit, pink-tinted wire-rim glasses and a kerchief the color of fresh blood. “The priests and the nuns I grew up with taught me that. They always talked about Judas. A Judas is the worst person in the world.”The 72-year-old Cambridge resident did not look at his former pal, the short, trim 83-year-old Bulger of South Boston, sitting military straight at the defense table, and Bulger’s ice-blue eyes did not turn toward him.

So many Judases, so little time.

Whitey sees Martorano as a Judas for making a deal with the feds and testifying against the Irish gang boss, who’s pleading not guilty to involvement in 19 murders. Martorano sees Whitey as a Judas for his years as a snitch for John “Zip” Connolly, a Boston F.B.I. agent who was a Judas to the F.B.I. because he helped Whitey steer clear of trouble. (They were from the same ZIP code.) Whitey’s younger brother, William, who rose to be a political boss in Massachusetts, was a mentor to Connolly when he was a young man.

Martorano testified on Monday that when he learned that Whitey and Stevie “The Rifleman” Flemmi were F.B.I. informants, “it sort of broke my heart.” They were his children’s godfathers, and his youngest son, James Stephen, was named for them.

In a gravelly monotone, with utter aplomb, Martorano talked about those he had taken out with a shot to the temple or heart, between the eyes or in the back of the head — plus several who were hit by mistake, including a teenage boy and girl.

In a sneering cross-examination Tuesday, Henry Brennan, a lawyer on Whitey’s defense team, referred to Martorano’s deal for a “so-called sentence” of 14 years (12 served) for 20 murders and asked the Executioner if he felt he was killing out of honor and integrity.

“I thought both,” Martorano replied.

Brennan sarcastically asked, “And that makes you a vigilante like Batman?”“I would rather be considered as a vigilante than a serial killer,” Martorano answered, adding: “A serial murderer kills for fun. They like it. I didn’t like doing any of it. I didn’t like risking my life either. I never had any joy, never had any joy at all.”He doesn’t consider himself a hit man either, even though the book he wrote with the Boston Herald columnist Howie Carr, which has been sold to Hollywood, is called “Hitman.”“There was no talk about money for murder, ever,” he said primly.

On the lam in Florida from charges of horse-race fixing and racketeering, he flew to Tulsa, Okla., in 1981 to kill a stranger, Roger Wheeler, the owner of World Jai Alai, as a favor to his friend John Callahan, who had been president of World Jai Alai and who was worried that Wheeler suspected him of skimming money from jai alai frontons. (Martorano described the sport as “a game they throw a racket around, a ball around, a Spanish game, I believe.”)He shot Wheeler in his car at a country club after he came off the golf course, and Callahan rewarded the Executioner with $50,000 for the Winter Hill pot. But it was not a quid pro kill, Martorano explained with gangsta gall: “He gave me that money in appreciation for me risking my life for him so that he wouldn’t go to jail.”The following year, his old friends Whitey and Stevie wanted Martorano to kill his new friend Callahan and blame it on the Cubans in Miami; they were afraid Callahan, whom they considered a wannabe gangster, would fold and finger the gang for killing Wheeler. Martorano later said he “felt lousy” about having to “kill a guy who I had just killed a guy for.” It was so “distasteful,” he said, that he never murdered anyone else. (He slyly hinted on “60 Minutes” that he might make an exception for Whitey.) The lawyers did their best to make sure everyone understood the criminal argot peppering the testimony. They had Martorano explain the meaning of a boiler (a stolen car), a crash car (a car that can slow down or bump a police car), a throw-off (planting evidence to throw off the investigation to go a different direction) and even a gang.

“What was a gang?” asked the prosecutor.

“A group of guys that got together and formed a gang,” Martorano replied.

“For what purpose?” the prosecutor asked.

“Illegal purposes,” the Executioner explained.