Notorious Irish-American gang boss James 'Whitey' Bulger has been arrested in California after spending years on the run.
He was captured in an apartment in Santa Monica after a tip-off, authorities said.
Bulger had been on the run for 16 years. His long-time girlfriend, Catherine Greig (60), was also detained. They are due to appear in court later today.
Eighty-one-year-old Bulger was on the FBI's 10 Most Wanted list for his alleged role in 19 murders, and had been involved in gun-running for the IRA. He was also a top FBI informant.
On Monday, the FBI launched a national ad campaign seeking information on the couple, focusing particularly on Greig, a dental hygenist. This campaign led to the tip-off, a spokesman said.
The authorities had offered a $2m reward for Bulger's capture.
The couple were living on the third floor of The Princess Eugenia, a three-storey apartment block close to the Pacific Ocean. Neighbours said they hadn't stood out as unusual.
Barbara Gluck, who lives on the same floor as Bulger and Greig, said she didn't know their names but recognised them after she saw news of their arrest.
Gluck described Greig as "sweet and lovely" and said they would have "girl talk" when they ran into each other. However, Gluck claimed Bulger became angry whenever he saw the two of them talking, and would tell Greig to "Stop talking".
"He was nasty," she added. "At one point, she [Greig] said he [Bulger] has a rage issue."
He was the leader of the Winter Hill Gang in Boston when he fled in January 1995 after being tipped off by a former FBI agent that he was about to be indicted.
Over the years, Bulger became a huge source of embarrassment for the FBI after the extent of his crimes and the agency's role in overlooking them became public. He was regarded as particularly vicious and was wanted on 19 counts of murder, drug dealing, extortion, money laundering and conspiracy.
He also helped to organise a seven-ton shipment of guns to the IRA in the 1980s. This led to the arrest (and subsequent imprisonment) of Sinn Fein TD Martin Ferris on board the gun-running ship Marita Ann off the Kerry coast in 1984.
Prosecutors said he went on the run after being warned by John Connolly Jr, an FBI agent who had made Bulger an FBI informant 20 years earlier. Connolly was convicted of racketeering in May 2002 for protecting Bulger and his cohort, Stephen 'The Rifleman' Flemmi, also an FBI informant.
Bulger provided the Boston FBI with information on his gang's main rival, the New England Mob, in an era when bringing down the Mafia was one of the FBI's top priorities.
Bulger was born in Boston to Irish parents and quickly rose to become the most powerful Irish-American criminal in Boston in the 1970s, mainly because of the protection deal he struck with the FBI. He was involved in gun-running for the IRA but made many enemies by informing on other Irish criminals, usually his enemies.
Bulger had planned for life on the run by leaving cash in safe deposit boxes around the world, including Ireland.
Bulger's brother, William M Bulger, is the former president of the Massachusetts state senate and the University of Massachusetts. He has admitted he had a telephone conversation with the fugitive shortly after he fled but testified before a congressional committee in 2003 that he had no idea where he was hiding. Another brother, John 'Jackie' Bulger, a retired clerk magistrate at Boston Juvenile Court, spent six months in prison for lying to federal grand juries about contacts with his brother.
Over the years, Bulger, who was the inspiration for the 2006 Martin Scorsese film 'The Departed', became a huge source of embarrassment for the FBI after the extent of his crimes and the agency's role in overlooking them became public.