Robert Hanssen: Convicted US spy found dead in Colorado prison

Robert Hanssen, 79, a former FBI agent who admitted to spying for Moscow, has been found dead in prison.

He was discovered unresponsive at a maximum-security facility in Florence, Colorado, on Monday morning.

Hanssen, sentenced in 2002 to life in prison for espionage, had received more than $1.4m in cash, diamonds, and money paid into Russian accounts.

He was living at the time in a modest four-bedroom house in suburban Virginia with his wife and six children.

Hanssen became an FBI officer on 12 January 1976, but is now known as the most damaging spy in the bureau's history.

Because of his counterintelligence role, he had access to classified information and in 1985 he started his criminal activity, sending information to Russia and the former Soviet Union.

He used the alias "Ramon Garcia" when corresponding with them.

According to the FBI's website, he "compromised numerous human sources, counterintelligence techniques, investigations, dozens of classified US government documents, and technical operations of extraordinary importance and value".

While there was some suspicion around his unusual activities occasionally, he was not caught for years.

After the spy Aldrich Hazen Ames was arrested by the FBI in 1994, the bureau realised classified information was still being leaked, which is what instigated the investigation into Hanssen.

He was slated to retire soon so the FBI acted fast in an effort to catch him "red handed".

"What we wanted to do was get enough evidence to convict him, and the ultimate aim was to catch him in the act," said Debra Evans Smith, former deputy assistant director of the Counterintelligence Division.