“Whether investigating a terrorism conspiracy or trying to bust a burglary ring, authorities depend on insiders willing to share information,” says the Los Angeles Times. “Yet dealing with informants is a treacherous business. Sometimes … they mislead their handlers. Sometimes they seduce them. Sometimes they corrupt them. And sometimes, they turn the tables, leaking state secrets to foreign governments.”
The Times recounts a series of problems with informants in federal investigations, incuding the pending Katrina Leung spy case.
FBI field offices review files on informants every 90 days. Every 18 months, they conduct internal inspections that include a look at informants. Every three years, each FBI office is visited by agents from headquarters, who review the files of every criminal informant and intelligence asset. Still, the secrecy inherent in handling informants makes it difficult to discover problems at an early stage.