A former professional gambler told jurors at the James " Whitey" Bulger trial how he survived a gunfire attack that decapitated a passenger in his car.
Mr Bulger, who had been on the run for 16 years, faces a life sentence for the murders in a sensational trial that has riveted Boston and attracted large crowds.
Frank Capizzi, 78, testified he was on his way to see his mother in Boston's North End when a torrent of gunfire struck the car he was in, riddling him with lead and decapitating one of his friends.
Mr Capizzi said: "I was hit in the head and could feel warm blood running down my neck,"
Mr Capizzi said he reached for a fellow passenger "and my hand went into his neck where his head should have been," he added.
Witnesses, including former Winter Hill Gang member John "The Executioner" Martorano, have sought to link Mr Bulger to the bloody trail of killings that haunted the city for decades.
Mr Bulger, 83, is charged with killing or ordering the murder of 19 people as head of Boston's Winter Hill crime gang in the 1970s and 1980s.
Mr Bulger has pleaded not guilty to all charges. If convicted, he faces the possibility of life in prison.
The trial has transported jurors back to an era when machine-gun-toting gangsters shot each other in phone booths and buried bodies under bridges in a bloody quest for control of the lucrative criminal underworld of drugs dealers and bookies.
Prosecutors have paraded an arsenal of assault weapons through the courtroom that ballistics experts said were seized from Winter Hill Gang members and their associates.
The guns ranged from World War Two-era automatic rifles called 'grease guns' to pocket-size revolvers.
Mr Martorano, who confessed to 20 murders but received a lenient 12-year sentence for testifying against his former partners, said earlier this week he preferred a snub-nosed .38 revolver for late nights at the clubs.
Two family members of alleged victims of the Winter Hill Gang also spoke including Joseph Angeli, who said he found out his father was killed on his 14th birthday.
Mr Martorano previously testified that he killed Mr Angeli's father, Joseph Notorangeli, in 1974 under orders from Mr Bulger who believed the man had killed a mafia ally.
Testimony from Mr Capizzi, a white-bearded man with dark sunglasses, was some of the most riveting to date in what is expected to be a four-month trial.
Mr Capizzi agreed to testify after he was granted immunity by US District Judge Denise Casper.
He has said he suspects the shooters who injured him on 19 March 1973, were from the Winter Hill Gang.
Mr Capizzi admitted under cross examination that there were several other criminal groups operating in Boston's North End at the time.
He said doctors removed 11 bullets from his back during a four-hour operation after the shooting, but left many others in.
Mr Bulger fled Boston after a 1994 tip from a corrupt FBI agent that arrest was imminent.
He evaded arrest for 16 years before law enforcement caught up with him living in hiding in Santa Monica, California on 22 June 2011.