Ambassador M K Bhadrakumar discusses possible U.S. intelligence links of Mumbai terrorist David Coleman Headley in an article in Asia Times. According to Bhadrakumar he "had a criminal record in the US from 1989 as a conspirator to import heroin and spent a total of six years in prison as a result of four convictions. He was later recruited as an agent by US drug-enforcement authorities, who after the 9/11 attacks in the US coordinated closely with the Central Intelligence Agency."
Chicago Resident David Coleman Headley Pleads Guilty to Role in India and Denmark Terrorism Conspiracies.
Other articles on the web such as this one claim that he was a U.S. Drug Enforcement(DEA) agent for many years.