The Middlesex District Attorney's Office says Stephen Rakes was found dead Wednesday afternoon in Lincoln, Mass., with no obvious signs of trauma to his body.
Authorities are conducting an autopsy to determine the 59-year-old Quincy man's cause and manner of death.
Prosecutors say Rakes and his former wife were forced to sell Bulger their South Boston liquor store in 1984 to use as a headquarters for his gang and as a source of legitimate income.
But another prosecution witness has testified that wasn't true, and it was unclear whether prosecutors would put Rakes on the stand.
Rakes had been attending the trial.
Take ABC13 with you!
Download our free apps for iPhone, iPad, and Android devices