"Ice cold" hitman John Martorano "highly credible" in Bulger trial, expert says

(CBS News) "Ice cold" convicted murderer John Martorano is a "highly credible" witness in the murder case of Boston mobster James "Whitey" Bulger, CBS News legal analyst and commentator Rikki Klieman said on "CBS This Morning."

"60 Minutes": Martorano: I'm a "government witness" not a "rat"

The hit man's testimony, Klieman said, though appalling, is very strong.

"He goes murder by murder by murder as if he were buying groceries. 'You take the eggs, I'll take the milk.' 'I stabbed him, I shot him. I killed him.' He is right now highly credible and terribly frightening, as if you were watching 'The Sopranos' or 'Goodfellas,'" Klieman said.

Former hitman testifies at "Whitey" Bulger trial

Martorano, now 72, served 12 years in prison after striking a cooperation deal with prosecutors. He was released in 2007.

However, the cross-examination of Martorano coming up is going to be critical for defense attorney J.W. Carney, Klieman noted, because he has to show that the government will stop at nothing to convict "Whitey" Bulger.

"Not only is this guy on the street after committing at least 20 murders," she said, "he's a guy who's made money from the government and from other people with a book and a movie."

Watch Elaine Quijano's report on the Bulger case in the player below.

Also, just because he's a bad guy, according to Klieman, his credibility may be undermined. She explained: "He can put Whitey in the midst of 11 of 19 that he's charged with, but ultimately, you have three bad, bad people, stone-cold killers sort of testifying against Whitey. This is the first of the three.

"What we know, though, is Whitey may not care about these counts. He may say, 'It's OK to get convicted,' but ultimately, always remember, it's the conviction about the two women that Whitey says, 'No, I didn't do those.' Maybe these, he might say he did," Klieman said.

The other two killers to take the stand in Bulger's case will be Stephen Flemmi, who is serving life in prison, and Kevin Weeks, who served five years and three months in prison.

For more with Klieman, watch her full interview in the player above.