Paul F. Markham, who dived into dark waters to try to find a young woman who was in a car with Senator Edward M. Kennedy when Mr. Kennedy famously drove off a bridge in Chappaquiddick, Mass., in 1969, died on July 13 in Peabody, Mass. He was 89.

His death was announced by the Gately Funeral Home in Melrose, Mass.

Mr. Markham, a former United States attorney for Massachusetts, had a long legal career. He prosecuted organized crime figures, including Raymond Patriarca, the boss of the New England Cosa Nostra. He was part of the Justice Department team in 1968 that prosecuted Dr. Benjamin Spock, the famed child-rearing expert, on charges of advising young men on how to evade the draft during the Vietnam War. (Dr. Spock was convicted but the verdict was overturned on appeal.)

But Mr. Markham, a longtime Kennedy family friend, was perhaps best known for having been swept up in the tragedy known as Chappaquiddick, named for a tiny island off Martha’s Vineyard.

On July 18, 1969, Senator Kennedy drove off a bridge on the island in an accident that killed the young woman, Mary Jo Kopechne, and effectively derailed his presidential ambitions. The name of the island would enter the political lexicon as shorthand for a permanent stain on Mr. Kennedy’s character, despite the subsequent achievements of his long Senate career.