Robert Hanssen was one of the most damaging spies in the history of the FBI. The former US agent, who has died in prison, leaked top secrets to Moscow for nearly 20 years - betrayals that the agency says cost lives. It took 300 agents to finally bring him down. Two of them who played a central part tell us how they did it. In December 2000, FBI agent Richard Garcia had a curious visit from a colleague overseeing the Russia desk. "He asked, 'Do you know a guy named Robert Hanssen?'" Mr Garcia recalled. "I said, 'No'." The official...