Robert Hanssen espionage case (2001)
FBI counterintelligence agent Robert Hanssen was arrested in February 2001 after spying for the Soviet Union and Russia for 22 years. He sold thousands of classified documents and compromised US intelligence operations, including double agents and technical collection programs.
Hanssen pleaded guilty to 15 counts of espionage and was sentenced to life without parole.
The case prompted sweeping reforms in FBI counterintelligence and internal security procedures.
Like Hanning, Hanssen was a trusted insider who passed classified information to a foreign power for years before being caught.
