A key terror suspect who allegedly helped to plan last year's attacks in Mumbai and plotted to strike Europe was an American secret agent who went rogue, Indian officials believe. David Headley, 49, who was born in Washington to a Pakistan diplomat father and an American mother, was arrested in Chicago in October. He has denied the charges. He came to the attention of the US security services in 1997 when he was arrested in New York for heroin smuggling. He earned a reduced sentence by working for the US Drug Enforcement Agency (DEA) infiltrating Pakistan-linked narcotics gangs. Indian investigators, who have been denied access to Mr Headley, suspect that he remained on the payroll of the US security services - possibly working for the Central Intelligence Agency (CIA) - but switched his allegiance to LeT. India is looking into whether Headley worked as a double agent," an Indian Home Ministry official said yesterday. Mr Headley, who changed his name from Daood Gilani, was in Mumbai until two weeks before the attacks on the city. Despite being firmly on the radar of the US intelligence agencies, he was allowed to return to India as recently as March. Indian officials are furious that their American counterparts did not share details of that visit at the time. The Indian media has raised the possibility that Mr Headley was being protected by his American handlers - a theory that experts say is credible.