Ex-FBI agent Robert Hanssen who spied for Russia dies in US jail

Robert Hanssen, who the FBI says began selling classified information to the Soviet Union in the mid-1980s, was sentenced to life in prison in 2002 [File: AP Photo]

Robert Hanssen, a former FBI agent turned spy whom the bureau describes as the most damaging in its history, was found dead in his prison cell, United States authorities have said.

Hanssen, 79, was sentenced in 2002 to life in prison after pleading guilty to spying for the Soviet Union and later Russia for more than 20 years.