A courtroom sketch depicts James "Whitey" Bulger during a pretrial conference in a federal courtroom Monday, June 3, 2013 in Boston, Mass. (Jane Flavell Collins/(AP Photo)

Lenient Deal for Bulger's 'Executioner' Was Worth It, Prosecutor Says

John Martorano spent just 12 years in prison, despite admitting to 20 murders.

A courtroom sketch depicts James "Whitey" Bulger during a pretrial conference in a federal courtroom Monday, June 3, 2013 in Boston, Mass. (Jane Flavell Collins/(AP Photo)

A courtroom sketch depicts James "Whitey" Bulger during a pretrial conference in a federal courtroom in Boston, Mass., June 3, 2013.

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Among the hit man's many victims were two teenagers riding inside a car with a target, who also died. He also admits he killed the wrong person on at least one other occasion.

[READ: Judge Rejects Bulger's 'License to Kill' Defense]

During opening statements last week, Bulger's attorney J.W. Carney vigorously denied that his client was an FBI informant and said Connolly, the corrupt agent, fabricated details in Bulger's FBI informant file.

"Number one, James Bulger is of Irish descent," Carney said. "And the worst thing an Irish person could consider doing is becoming an informant."

During cross-examination Tuesday, Martorano said he never accepted money for killing people and was just helping out his friends.

"I always tried to be a nice guy," he said. "Serial killers kill for fun, they like it, I don't like it ... never had any joy. Serial killers kill until they get stopped, I stopped and confessed my problems." Like Bulger, who was arrested in 2011 after 16 years in hiding, Martorano was on the run for years until he was arrested in 1995.

After Tuesday's court proceedings Carney told reporters he was very pleased with the defense's grilling of Martorano. "The cross examination by my co-counsel Hank Brennan is the very best cross examination I've seen by any lawyer in the past 35 years," he told reporters, according to NECN-TV.

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