The US jury hearing the murder and racketeering trial of James "Whitey" Bulger has entered a fourth day of deliberations on whether to convict the former mob boss.

Mr Bulger, 83, faces a sweeping 32-count indictment that could leave him in jail for the rest of his life.

As well as murder and racketeering charges, Mr Bulger is also charged with extortion, money laundering and drug trafficking dating back to his years running Boston's feared Winter Hill crime gang in the 1970s and '80s.

The man who inspired the character played by Jack Nicholson in Martin Scorsese's 2006 Academy Award-winning film "The Departed" has pleaded not guilty to all charges.

His attorneys did concede he was a drug dealer, extortionist and loan shark, in essence an "organized criminal."

US District Judge Denise Casper has urged the 12 jurors to reach unanimous verdicts on all the charges, including 19 murders Mr Bulger is accused of committing or ordering.

Prosecutors said corrupt FBI agents sharing Mr Bulger's Irish background turned a blind eye to his gang's crimes in exchange for information they could use against the Italian Mafia.

But Mr Bulger, along with pleading not guilty to the crimes he was charged with, insisted he also was not "a rat."