An investigation by ProPublica and FRONTLINE during the past year did not find proof that Headley was working as a U.S. agent at the time of the attacks. But it did reveal new contradictions between the official version of events, Headley’s sworn testimony and detailed accounts of officials and others involved in the case. The reporting also turned up previously undisclosed opportunities for U.S. agencies to identify Headley as a terrorist threat, and new details about already-reported warnings.
Splat!
Trying to stop him? Perhaps they should have stopped paying him. They were not trying to stop him.
Note that they say they didn't find "proof". At what points evidence rises to that level is a subjective thing, but certainly there is plenty of evidence that he was US intelligent asset at the time of his involvement in the Mumbai terror attack. In fact, outside of Frontline and ProPublica it is hard to find anyone who denies it. The question is whether he was acting on orders from his handlers or on his own.
And the answer of course is the former. Otherwise one would have to believe he thought he could participate in one of the largest terror attacks in history without being exposed by the subsequent investigation. Moreover, if it were LeT who executed the attack, and assuming they are not a Western intelligence front, what need would they have for Headley? If they had a mole this far up the food chain, would they imperil him for the low-level function in the Mumbai Massacre of which he is accused? Not a chance.
ProPropagandica has been spinning this story on the government's behalf for some time now. It's classic journaganda: They pretend to be exposing government lies while reinforcing the ones that matter. The first job of government is perception management, and ProPublica is doing its part.
http://www.propublica.org/article/david-headley-homegrown-terrorist