It's a theory that's being discussed in international media, and was brought up in Parliament on Tuesday - that David Coleman Headley, the American national arrested for Mumbai's 26/11 attacks- was a CIA agent who went rogue.

Now, Indian intelligence sources tell NDTV that they've suspected for a while that David Coleman Headley was a CIA agent.

Indian officials say they've complained to the FBI that it should have shared information about Headley with India during Headley's last trip to India in March this year.  That would have allowed India to track his movements, and to arrest him.

The FBI has confirmed that it was monitoring Headley for at least a year before he was arrested in October this year.   He was already under surveillance when Mumbai's 26/11 attacks took place  - attacks that Headley helped to plot and execute, according to the charges against him in a Chicago court.  Many experts have pointed out that the FBI had alerted India to a strike against its hotels before 26/11 - the warning was so specific that it actually named the Taj - so it's odd that Headley's name was never passed on as a part of this warning.

In the international media, especially The Daily Beast and The New York Times, there have been reports that Headley was a CIA agent who went rogue.  He was possibly used by America's Drug Enforcement Administration to infiltrate Pakistan's narcotics underbelly. From there, did Headley move to the CIA?  That's a story that NDTV has reported on in the last two days.

Indian investigators say that Rahul Bhatt, the son of director Mahesh Bhatt, who was befriended by Headley during his trips to Mumbai, has also said that Headley often talked about commandos and wars. This, Bhatt is reported to have told officials, made him wonder if Headley was an American spy.

What could help India's National Investigation Agency (NIA) to get some more information on Headley's real identity is tracking the money he spent.  Headley seemed to have large funds at his disposal. The NIA is looking into who deposited money into Headley's bank accounts.  

In the Rajya Sabha on Monday, CPM MP Brinda Karat raised the issue of why Indian officials have been denied access to Headley after his arrest.  A team of officials who travelled to Chicago were not allowed to question Headley.  And America has since said that it's "too premature" to discuss Headley's possible extradition to India.  That's an odd response, say Indian officials, given that Headley stands charged of plotting India's worst terror attacks.