Undercover American narcotics agents have laundered or smuggled millions of dollars in drug proceeds as part of Washington’s expanding role in Mexico’s fight against drug cartels, according to current and former federal law enforcement officials.

The high-risk activities raise delicate questions about the agency’s effectiveness in bringing down drug kingpins, underscore diplomatic concerns about Mexican sovereignty, and blur the line between surveillance and facilitating crime.

Ten years after the attack, an in-depth examination of the case against Ivins by PBS’ “Frontline,” McClatchy Newspapers and ProPublica raises fresh doubts about the government’s evidence and questions whether - despite a $100 million investigation - the real anthrax killer remains on the loose.