Boston mobster James 'Whitey' Bulger will see his old partner in crime for the first time in two decades when admitted killer Stephen 'The Rifleman' Flemmi takes the stand in Bulger's murder and racketeering trial.  

The two former leaders of the Winter Hill Gang have not seen each other since 1994 when Mr Bulger fled Boston to evade arrest.

Their tale recalls a dark side to Boston's FBI during that period.

Both men were listed as FBI informants but also were given tips by corrupt agents who helped them escape capture and root out "snitches" within their ranks.

Their story inspired the 2006 Academy Award-winning film "The Departed," in which Jack Nicholson played a character loosely based on Mr Bulger.

In 2004, Mr Flemmi pleaded guilty to 10 murders in a deal that spared him the death penalty.

His testimony is expected to make up the backbone of the government's case against Bulger, who is charged with killing or ordering the killing of 19 people.

If convicted, Mr Bulger, now 83, could get life in prison.

In six weeks of testimony, witnesses so far have described Bulger as a cold-blooded criminal quick to violence.

From the witness stand, former associates have accused him of participating in killing several people suspected of talking to law enforcement.

Others said he used fear to extort cash.

Yesterday, a former drug kingpin testified that Mr Bulger forced him to play Russian roulette in a nightclub's back room in 1983 as a way to make him hand over $1m and then later threatened to "cut my head off".

Mr Bulger has pleaded not guilty to all charges, but through his lawyer has admitted being an extortionist, drug dealer, loan shark and "organised criminal."

Mr Bulger's trial has riveted Boston and given the jury a glimpse of an era when machine-gun toting mobsters shot associates and 'rats' who talked too much and buried bodies under bridges.

Jurors yesterday also got a detailed description of how his gang used fishing boats and freighters in the 1980s to smuggle drugs into the US.

They also shipped guns to the Irish Republican Army which were used during the Troubles.

Mr Bulger rose from his youth in a housing project to become the most feared criminal in Boston.

After a 1994 tip from a corrupt FBI agent that arrest was imminent, Bulger fled.

He was finally captured in Santa Monica, California, in 2011 after 16 years on the lam.