Double agent Robert Hansen, the subject of one of America’s most devastating spy cases, died Monday at the age of 79 in the prison where he has been held since 2002, the US Prison Service said.

A counterintelligence officer in the federal police, he began working for the Soviets during the Cold War and leaked some of America’s best-kept secrets to Moscow in the 1980s and 1990s for $1.4 million and diamonds.

According to the FBI website, Robert Hansen was “the most destructive spy in FBI history.”

He was found unconscious yesterday morning in his cell at a maximum security prison in Florence, Colorado, where he was serving a life sentence. According to the prison service, attempts by employees to return him were in vain.

Robert Hansen, a former police officer from Chicago, joined the FBI in 1976. A few years later, he joined counterintelligence in New York, where he was tasked with hunting down Russian spies on American soil and recruiting Soviet diplomats for the UN.

Taking advantage of this key position, he voluntarily offered his assistance to the USSR intelligence services, using the pseudonym “Ramon Garcia”, while his handlers did not know his identity.

From his positions in New York and then Washington, he handed over 6,000 pages of documents, including military plans, counterintelligence information, and the names of double agents working for the US, first to the Soviets and then to the Russians.

Although the FBI was aware that there were “moles” in its ranks – in the language of intelligence – Robert Hansen remained unsuspicious for many years. Married, father of six children, he lived a low profile, always maintaining close relations with the capital’s Catholic elite.

But in 2000, he was handed over by a Russian defector. After being followed, he was finally arrested in 2001 while preparing to hand over classified documents meant for Russian agents in a park in Virginia.

He avoided the death penalty by agreeing to cooperate with the investigation. After he admitted that he acted out of selfish motives, he was interrogated for about 200 hours. In 2002, he was sentenced to life in prison without the possibility of parole.