Confessed hit man John Martorano proclaimed defiantly in a Boston courtroom Tuesday that he is "no serial killer," even though he has admitted to rubbing out 20 people, including innocent bystanders.
The 72-year-old federal witness, known as "the Executioner," testified against his alleged former mob boss, James "Whitey" Bulger, 83, and claimed he was an FBI informant.
Martorano insisted he was no "mass murderer" and preferred to be called a "vigilante" who nobly protected friends and family.
Martorano rationalized the killings by saying the code he learned was, "family and friends comes first."
But criminologists said that even though Martorano, by his own testimony, is "technically" a serial killer -- one who kills one at a time over weeks, years or decades -- his self-described motivation and execution doesn't fit the mold of a Ted Bundy or a Jeffrey Dahmer.
"A serial killer typically uses sex as a vehicle for tempting to gain a sense of power and dominance and control," said Jack Levin, a professor of criminology at Northeastern University in Boston and a co-author of the 2008 book, "Extreme Killing."
"In most cases, it includes torture," he said. "Martorano was right in court when he suggested that a typical serial killer enjoys his work. The more he makes the victim feel inferior, the more superior he feels. And so he tortures and sodomizes and dismembers and eviscerates and strangles his victim, taking the last breath from his dying body. That's what makes them feel so good."
Martorano, who has been a free man since 2007 after he cut a deal with the government to testify against Bulger, testified, "I didn't enjoy killing."
Levin said criminologists might agree the term is misused when it comes to gangland killers.
"Those who study serial murder are concerned about overusing the term and that it becomes diluted and loses its value," he said.
He theorized that those in organized crime are more like "domestic terrorists."
"What happens is a mobster terrorizes a community so that he gets shopkeepers and others to comply," said Levin. "He used terror in a way that is politically motivated."
He compared Martorano and his partners in crime to the Washington, D.C., snipers who had the city in "the grip of terror" to make $10 million.
"It's not an end -- it's a means or tactic used by some criminals for personal gain," he said.
Bulger, one of Boston's most notorious alleged criminals in the 1970s and 1980s, purportedly head of the predominantly Irish-American so-called Winter Hill Gang that was portrayed in the Hollywood film, "The Departed," faces a 32-count indictment.
Gangsters like Martorano, and perhaps Bulger, may rationalize murders as "honor among thieves," with a code of rules and behavior. For example, the code prohibits the killing of women, according to testimony in the Bulger trial.
"Is there any honor or integrity in what you did?" Martorano was asked under cross-examination on Tuesday by Henry Brennan, a defense lawyer.
"I thought so," he replied.
Ethics are rarely a motivator, except on television. The serial killer "Dexter" has a lust for killing, according to Levin, but he has a code of ethics -- killing those who have wronged others.
"He's an outlier," said Levin. "But I don't like him for a different reason. He is an antihero and that really bothers me -- someone who kills a large number of people and can easily justify it in an attempt to rid the world of evil."
Some serial killers, like Ted Bundy, target prostitutes, believing they are "doing the world a service."
Levin speculated that Martorano might be more like landlady Dorothea Helen Puente, who in the 1980s killed for profit. She ran a boarding house in Sacramento, Calif., and cashed the Social Security checks of nine elderly and mentally disabled boarders.
Martorano rationalized his murders as acts to protect family and friends, even citing the values that stemmed from the "troubles" between factions in Northern Ireland.
"Most people in Northern Ireland never killed anyone," said Levin. "I have been there twice and they are a gentle, decent people and not serial killers."
Bulger's defense attorney, J.W. Carney, called Martorano a "criminal psychopath."
"He would kill people almost randomly," Carney said. "He would kill people as easily as we would order a cup of coffee. ... The federal government was so desperate to have John Martorano testify ... they basically put their hands up in the air and said, 'Take anything you want.'"
Experts consulted by ABCNews.com agreed that Martorano and other gangland criminals could suffer from a personality disorder, lacking conscience and empathy.
"We had a lot of problems with people," Martorano testified. "And you know, you just killed them before they kill you. It's kill or get killed, at times."
Kenneth V. Lanning, a retired special agent at the Behavioral Science Unit at the FBI's National Center for the Analysis of Violent Crime, said there is a difference between being psychotic, which is a mental illness, and being a psychopath, which is considered a legally culpable disorder.
"Lay people and the media constantly confuse and interchange the terms psychotic and psychopath, and occasionally throw in psycho to make it worse," he said. "Schizophrenia is an example of illness that causes psychosis. By definition, those who are psychotic have hallucinations, delusions and disordered thinking, or a combination of these."
Psychosis sometimes reduces a person's responsibility for a crime with court findings of "insanity," "diminished capacity" or "guilty but mentally ill," according to Lanning.
But being a psychopath involves a personality disorder, he said.
"It is not something you have, it is what you are," said Lanning. "Psychopaths know others consider what they are doing wrong. They just don't care."
Psychopaths, often excellent liars and con arts, are also held responsible for their criminal behavior, according to Lanning.
"If they were not held responsible for their criminal behavior," Lanning said, "there would not be many serious criminals left in prison.
"As they lie to you, they can look you right in the eye, swear on a stack of Bibles, and not blink an eye," he said. "They lie for the same reasons everyone lies -- the truth is damaging or embarrassing. They also lie for reasons that most people do not -- just to see if they can get away with it and to play with people."