Boston (CNN) -- Portraying a star government witness as a mass murderer, a serial killer and a liar without remorse, defense lawyers for James "Whitey" Bulger tried Wednesday to undermine the testimony of that witness, former mob hitman John Martorano.
"You lied to your friend John Callahan didn't you?" asked defense lawyer Hank Brennan, referring to a man Martorano shot dead.
"That was a necessity," said the confessed killer. "I told John I wanted to see him. I couldn't tell him I wanted to shoot him."
Martorano wrapped three days of detailing murders he allegedly committed with Boston's most feared former mob boss, Bulger, by confirming to prosecutors that together he and Bulger were involved in 11 murders. Bulger had admitted to others he'd committed on his own, Martorano said.
Bulger is charged with 19 murders as well as racketeering and extortion. He was arrested in 2011 after living in hiding for 16 years and landing on the FBI's most wanted list.
At times, Martorano seemed to parse his testimony during cross-examination. Asked about one murder, he said of the victim, "I stabbed him. I didn't kill him." After a pause, he added, "Not until later."
Martorano also testified that even though Bulger was older by a decade, "He wasn't my boss." Still, the former hitman acknowledged there were times he would do whatever was needed, no questions asked, because Bulger "knew the right buttons to press."
Earlier Martorano alluded to Bulger as "Judas," which he described as "a person like an informant, a rat, a no-good guy. I was brought up that that was the worst thing in the world."
Although Bulger's lawyers tried to highlight inconsistencies in Martorano's testimony, he didn't waiver, declaring he hadn't lied to prosecutors since cutting a deal that guaranteed his testimony in exchange for a 14-year sentence.
He said he knew if he lied, "They'd break the deal," and send him back to prison. Martorano was released from prison in 2007 after serving 12 years.
Defense attorney Brennan compared Martorano to another hitman, Joseph Barboza, who may have killed as many as 26 people beginning in the 1960s. Brennan told jurors Barboza was also a government informant and that he lied under oath.
"The government protected him," said Brennan, referring to Barboza
Not missing a beat, Martorano quipped back, "Not too good," referring to Barboza's ultimate death once he was outed as a "rat."
Martorano admitted in court Wednesday that he gave false statements during the time his deal with prosecutors was being drawn up, adding that only after deciding to cooperate with the government did he begin telling the "whole truth" about the criminal enterprise and his associates.
"After I made an agreement with the government I never lied," Martorano said.