John Walker Jr., a former American sailor convicted during the Cold War of leading a family spy ring for the Soviet Union, has died in a prison hospital in North Carolina, officials said Friday.
He died Thursday at the Federal Medical Center in Butner, Federal Bureau of Prisons spokesman Chris Burke told the Los Angeles Times via email. Prison officials did not release a cause of death, and the North Carolina Medical Examiner's office had no immediate information on the cause of death. He was 77.
Walker was considered the ringleader of a spy ring that authorities at the time said was among the most damaging in U.S. history.
His brother Arthur J. Walker, who made $12,000 for selling classified documents to Soviet agents through John, died in the same federal prison in Butner, N.C., in July. He was 79.
John Walker Jr. was said to have throat cancer. He was set to be released in May, according to federal authorities.
When the family espionage ring was uncovered, John Walker Jr. was cast by authorities as its amoral mastermind, a manipulator who got his son, Michael, his older brother, Arthur, and his best friend, Jerry Whitworth, to join him.
Walker started spying in 1967 during his Naval career and sold the KGB "vital U.S. cryptographic secrets that had allowed Russian agents to decipher approximately one million coded Navy dispatches," wrote Pete Earley, author of "Family of Spies: Inside the John Walker Spy Ring."
His 18-year spying career was uncovered after his ex-wife, Barbara Crowley Walker, alerted the FBI in the midst of a custody battle between her daughter, Laura Walker Snyder, and her son-in-law, Mark Snyder.
Snyder admitted to The Times that he had once threatened to "disclose whatever I knew" about John Walker if his son was taken from him, but denied knowing any specifics about Walker being a spy. Fearing she might not ever see her grandson again, Crowley Walker went to the FBI, she testified.
John Walker Jr. later agreed to a plea deal, cooperating with federal authorities and testifying against Whitworth in exchange for securing a lighter, 25-year sentence for his son, Michael.