Middlesex District Attorney Marian Ryan told reporters Friday William Camuti, 69, was arrested in Boston on suspicion of the July poisoning death of Stephen "Stippo" Rakes, The Milford Daily News reported.
Ryan said Camuti and Rakes -- whom she described as longtime acquaintances -- met at a fast-food restaurant in Waltham July 16, and Camuti put poison in Rakes' coffee.
She said Camuti drove around for several hours before dumping Rakes' body in Lincoln where it was found July 17.
Although Rakes had been on the witness list for Bulger's murder and racketeering trial in Boston, Ryan said investigators believe Camuti acted alone. She said there is evidence Camuti owed Rakes a "significant amount" of money.