The following article on the Sam Melville-Jonathan Jackson Unit is an excerpt from Mel Ayton's Hunting the President: Threats, Plots, and Assassination Attempts-From FDR to Obama.
The Secret Service investigated at least two domestic political groups considered to be threats to President Jimmy Carter's life.
In March 1977, Carter was scheduled to give a “town hall” talk in Clinton, Massachusetts, a mill town thirty miles to the west of Boston. Shortly before his scheduled visit, a factory in a nearby town was bombed by the Sam Melville-Jonathan Jackson Unit, a radical leftist group with only a few members.
The group, named after two black radicals, was formed in the early 1970s by Thomas Manning and Raymond Levasseur, two Vietnam veterans who met in a Massachusetts prison. The group was responsible for at least nineteen bombings and ten bank robberies and the murder of a New Jersey state trooper. During Carter's presidency, the Sam Melville-Jonathan Jackson Unit undertook eight bomb attacks.
The March 1977 factory bombing in Marlboro was a protest against the president's upcoming scheduled visit. “While the president wines and dines,” a letter left at the scene of the bombing stated, “we remember our people who were brutalized in prison.” The bombers also phoned the Boston FBI office and told Agent Richard Bates that “there would be more bombings.” In addition to prison conditions and Carter's visit, the group's letter demanded the release of imprisoned Puerto Rican nationalist Oscar Collazo, who had been convicted of killing a White House police officer during the 1950 attempt on Truman's life, and the four Puerto Rican nationalists who had shot and wounded five congressmen in the House of Representatives in 1954.22
Levasseur was arrested on November 3, 1984. He was convicted and sentenced to forty-five years in prison. Manning got life for the murder of a New Jersey state trooper and fifty-three years for the New York City area bombings.