Robert Hanssen, 79, was "found unconscious" at 6:55 a.m. at the maximum-security federal prison in Colorado.
He was serving 15 consecutive life sentences for betraying the United States. Hanssen began spying for the Soviets in 1979, three years after joining the FBI. He pleaded guilty to selling thousands of classified documents over the years detailing U.S. strategies for nuclear war as well as counterintelligence information. He also revealed to Moscow bosses the existence of a secret underground tunnel built by the FBI under the Soviet embassy.