Robert Hanssen, a former FBI agent who spied for the Soviet Union and Russia in one of the most damaging espionage cases in American history, died Monday, officials said. He was 79.
Hanssen died around 7 a.m. after he "was found unresponsive" in his prison cell in Florence, Colorado, the Federal Bureau of Prisons said in a press release. "Responding staff immediately initiated life-saving measures...the inmate was subsequently pronounced dead by outside emergency medical personnel."
A cause of death was not released, but sources told The Associated Press that Hanssen was believed to have died of natural causes.
Hanssen had been incarcerated at ADX Florence, a federal supermax facility that is considered the most secure prison in the United States, since 2002. He had pleaded guilty in 2001 to espionage and other charges following a yearslong investigation into his actions, and was sentenced to life in prison without the possibility of parole.
Hanssen, a native of Chicago, joined the FBI as a special agent in 1976, and began spying for the Soviet Union just three years later. He would spy for Moscow during "some of the most consequential times for U.S. and [Soviet] relations and continuing past the end of the Cold War," CNN reported. During his time as a spy, Hanssen provided classified national security information in exchange for "more than $1.4 million in cash, bank funds, and diamonds," according to the FBI webpage documenting his case.
As an agent with counterintelligence clearances, Hanssen used encrypted codes, "dead drops," and a variety of other clandestine methods to provide information to foreign assets, according to the FBI. Investigators eventually caught and charged Hanssen, who would later apologize for his role as a spy during his sentencing. The FBI later dubbed Hannsen's years of espionage "possibly the worst intelligence disaster in U.S. history."