William F. Pepper, 86, Dies; Claimed the Government Killed Dr. King

William F. Pepper, who was the central figure in a decades-long effort to prove that the Rev. Dr. Martin Luther Jr. was killed not by a lone gunman but by a vast government plot, a controversial stance that made him something of a celebrity among the country’s teeming subculture of conspiracy theorists, died on April 7 in Manhattan. He was 86.

His wife, Mina Nguyen-Pepper, said the cause of his death, in a hospital, was pneumonia. He lived in Manhattan.

James Earl Ray shot and killed Dr. King in Memphis on April 4, 1968. He was arrested two months later at Heathrow Airport in London, just before boarding a flight to Brussels and eventually to Rhodesia (now Zimbabwe), which at the time was under white rule.

Mr. Ray pleaded guilty in order to avoid execution, and therefore did not go on trial. But he recanted soon after his conviction, and he spent the rest of his life claiming that he was innocent, himself a victim of a plot to kill Dr. King.

More than anyone else, it was Mr. Pepper, a lawyer, who kept Mr. Ray’s campaign alive long after Mr. Ray’s death in 1998. After taking on Mr. Ray as a client in 1988, he pressed the case across a variety of avenues, including courtrooms, the news media, a television special and three books.