On Wednesday, the FBI arrested notorious Boston gangster James “Whitey” Bulger and his companion in Santa Monica, California, after the couple averted authorities for more than 16 years. We asked Jack Levin, the Brudnick Distinguished Professor of Sociology and Criminology at Northeastern University, to assess the role of tipsters in capturing fugitives, the difficulty of living life on the lam and Bulger’s place among the world’s most notorious criminals.

This arrest came just three days after the FBI launched a widespread publicity campaign to solicit new leads to Bulger’s whereabouts. What role do tipsters play in catching fugitives?

Sometimes, law enforcement underestimates the willingness of ordinary citizens to assist in the apprehension of fugitives, not necessarily for a big reward but only out of compassion for the victims. Having said that, Whitey Bulger’s arrest is only one of a long list of murders, abductions and acts of terrorism that have [been solved] thanks to input from the public.

The television program America’s Most Wanted has helped the police arrest hundreds of fugitives, based on telephone tips from concerned viewers. The D.C. Snipers, who terrorized the East Coast for three weeks in October 2002, were caught thanks to a tip from a resident who spotted the killers’ car parked in a rest area off of Interstate 95. The Unabomber was arrested when his mother and brother recognized the writings in Theodore Kaczynski’s manifesto in the Washington Post and decided to inform the FBI.

Where does Bulger rank among the world’s most notorious criminals?

Bulger’s alleged body count — 19 — places him among the most notorious criminals in history. We tend to think of Bulger as a mobster, not a serial killer. Yet, he allegedly took numerous lives, not unlike David Berkowitz, also known as the Son of Sam (six victims), Dennis Rader, also known as the B.T.K. killer (10 victims) or John Wayne Gacy, also known as the Killer Clown (33 victims). Money or protection, not sexual sadism, may have been Bulger’s motive. But this does not exclude him from being called a serial murderer.

How does a fugitive for almost two decades go about living a so-called “normal” life?

In order to stay on the loose for 16 years, Bulger must have exercised extreme caution not to be identified. It will be interesting to determine whether he had plastic surgery, wore a disguise or dressed differently. His ability to blend into his environment may have depended on his connections with other residents. He must have had enough money to lead a normal life without attracting attention.

Other fugitives who avoided apprehension over a lengthy period were aided by friends and allies. Take, for example, Eric Rudolph, who planted a bomb at the 1996 Olympics in Atlanta and blew up abortion clinics and a gay nightclub. He managed to remain on the lam for five years, hiding in the hills of North Carolina and aided by shelter, food and money from residents who agreed with his politics.