He had been incarcerated in Arizona, Oklahoma and Florida, prison officials have said, without giving reasons for the moves.
Bulger arrived at the penitentiary on Monday after being processed at an Oklahoma City transfer site.
Bulger's attorney, Hank Brennan who tried to appeal his life sentence all the way to the U.S. Supreme Court, declined to comment to the Boston Herald pending notification of Bulger's death by the Bureau of Prisons.
When he was captured, Bulger was convicted in 2013 of partaking in 11 murders stretching from Florida to Oklahoma to MA. Bulger also served as the inspiration for Jack Nicholson's character Frank Costello in Martin Scorsese's 2006 film The Departed. Details of his death have not been announced. No other staff or inmates were harmed, said officials.
Bulger, nicknamed "Whitey" for his bright platinum hair, grew up in a gritty South Boston housing project and became known as one of the most ruthless gangsters in Boston.
In one of those heartfelt letters, Bulger wrote: 'My 16 years on the run were the happiest years of my life and hers. He was convicted in 2013 for a slew of crimes, including being linked to at least 11 murders.
Bulger was born September 3, 1929, in Boston. A high school dropout, Bulger began a life of crime that eventually led to prison stays at Alcatraz and Leavenworth. The bureau added him to its "10 Most Wanted Fugitives" list in 1999, offering $250,000 for information leading to his arrest.
'More time + fine than people who confessed to murder and made deal to testify against me for the gov and in return set free after short sentence.
She remains locked up at a women's prison in Minnesota.
Greig and Bulger started dating in the 1970s and lived together in Boston.
As they called him a coward, a rat, a punk and Satan, Bulger kept his head down and showed no emotion as he scribbled on a pad.