79-year-old Robert Hanssen was found on Monday unresponsive in his cell at the prison in the US state of Colorado where he was serving his life sentence, and was later pronounced dead, according to a statement from the prison.
Robert Hanssen, who worked for the FBI’s national security group for 27 years, passed around 6,000 pages of classified defense and intelligence information to the Soviet Union and Russia between 1979 and 1999. In exchange, he was paid in diamonds and $1.4 million in cash.
The documents exposed both spies working for the United States and internal security plans, and the information he leaked is believed to have cost at least three people their lives.
Hanssen was arrested in 2001 after leaving a bundle of secret documents in a park, where they were to be collected by his Russian contact. He later pleaded guilty to 15 counts of espionage and was sentenced the following year by a federal court to life in prison, without the possibility of parole.