Former FBI agent Robert Hanssen, convicted of spying for Russia, dies in federal prison

Robert Philip Hanssen, a former FBI agent who received more than $1.4 million in cash and diamonds for committing espionage on behalf of Moscow, has died in prison, the Federal Bureau of Prisons announced Monday.

Hanssen, 79, was found unresponsive Monday morning in his cell at a federal prison in Florence, Colorado, according to a statement from the Federal Bureau of Prisons.

"Responding staff immediately initiated life-saving measures. Staff requested emergency medical services (EMS) and life-saving efforts continued," the statement said. "Mr. Hanssen was subsequently pronounced deceased by EMS personnel."

He is believed to have died of natural causes, The Associated Press reported.

Hanssen had been serving a life sentence in the prison, which is a maximum security facility, without possibility of parole since 2002. Hanssen pled guilty to 15 counts of espionage and other charges in 2001, according to the FBI.

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The FBI was notified of Hanssen's death, according to the Federal Bureau of Prisons. The agency said no staff or other inmates were injured and there was no public danger.

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Who was Robert Hanssen?

Known as the most damaging spy in FBI history, according to the FBI, Hanssen had been spying for Russia and the former Soviet Union since at least 1985. He joined the bureau in 1976 and had years of experience and training as a counterintelligence agent.

"Hanssen went undetected for years, although some of his unusual activities had aroused suspicion from time to time," according to the FBI's history file of Hanssen. "Still, he was not identified as a spy."

The former FBI agent had provided highly classified national security information to the Russians in exchange for more than $1.4 million in cash, bank funds, diamonds, and Rolex watches.

According to the FBI, Hanssen held key counterintelligence positions while assigned to New York and Washington, D.C. His assignments allowed him to have "direct and legitimate access to voluminous information about sensitive programs and operations," the FBI said in 2001.

Investigators accused Hanssen of sharing extensive detail on U.S. counterintelligence techniques, investigations, classified government documents, and operations.

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Using the alias "Ramon Garcia" with his Russian handlers, authorities said Hanssen passed on "6,000 pages of valuable documentary material" and 26 computer disks. Officials believed Hanssen told his handlers about a secret tunnel the United States built under the Soviet Embassy in Washington for eavesdropping.

He was also accused of compromising numerous human sources, which confirmed the identities of Russian double agents. Officials said at least three Soviet officers who were working for U.S. intelligence were executed as a result.

According to the FBI, later investigations revealed Hanssen as a Russian mole and investigators said their "goal was to catch Hanssen 'red handed' in espionage." He was caught taping a plastic bag filled with classified materials to the underside of a footbridge in a park in a "dead drop" for Russian handlers in 2001.

Hanssen would later admit that he was motivated by money rather than ideology.

Contributing: The Associated Press