The presence of David Headley in Mumbai has thrown up many questions before investigators busy trying to find out whether disappeared cadres of the banned Student Islamic Movement of India and the Indian Mujahideen had used his immigration service.
Since Headley had set up his office in the metropolis in 2006-07, the central security agency sleuths were burning midnight oil to ascertain how many wanted militants had escaped during this period and whether they had used the services of Headley's immigration services, sources said.
Headley, who came to India nine times since 2006-07, had wound up the entire immigration business in April this year and the sleuths could not get any information about his functioning of business and clients.
The mysterious disappearance of many accused from Gujarat, Madhya Pradesh and Hyderabad including that of Rahil Sheikh, an alleged mastermind in the 2006 Mumbai serial blasts that left 187 people dead, was being looked into.
Sources said that after winding up the immigration office in Mumbai, Headley had rented out the space to someone else.
The 49-year-old Headley was arrested by the Federal Bureau of Investigation at Chicago's O'Hare International Airport, as he prepared to board a flight to Philadelphia and intended to travel to Pakistan.
The FBI also arrested Tahawwur Hussain Rana, 48, a Canadian citizen of Pakistani origin, for alleged involvement in terror activities.
Sources said the immigration forms of Headley were being dug out to ascertain further details including the people with whom the accused had got in touch upon his arrival in the country.
Both Rana and Headley were arrested by the FBI for planning to carry out terror acts in and outside the US with the help of Pakistan-based Lashkar-e-Tayiba.
During the interrogation, they told the FBI that they were planning to carry out terror attacks in India, which included hitting vital installations like National Defence College in Delhi and five-star hotels.
An Indian investigation team was sent to the US immediately to question the two accused.