A 65-year-old man pleaded guilty to killing Brian Watson, a South Boston man whose body was found on the side of Interstate 93 in Manchester in 1984.

Michael Lewis, also of South Boston, pleaded guilty to manslaughter, New Hampshire Attorney General John Formella and the members of state’s Cold Case Unit announced Tuesday.

Watson was 23 at the time of his slaying. After discovering his body, investigators identified him through dental records. However, they didn’t link Lewis to his death until 2022, when renewed effort by Massachusetts and New Hampshire law enforcement led to the indictment of Lewis, charging him with first-degree murder.

"Investigators determined that Lewis and another man, both involved in South Boston’s drug trade, fatally shot Mr. Watson in Boston and then transport

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