Former FBI agent Robert Hanssen, one of the most damaging spies in U.S. history, was found dead in his prison cell in the U.S. state of Colorado on June 5, prison officials said. The 79-year-old Hanssen was arrested in 2001 and pleaded guilty to selling highly classified material to the Soviet Union and then Russia. He was serving a life sentence. Hanssen began spying in 1979.
