The mystery soon deepened when ProPublica gained access to a trove of Snowden’s classified materials. Suddenly a new, previously hidden layer in the story emerged, one that largely contradicted the government’s claims and revealed Mumbai as a tragic case study in the strengths and limitations of high-tech surveillance – a rare look at how counterterrorism really works.
Our reporting airs tonight in “American Terrorist,” a major update of the 2011 Frontline film. It details the story of Headley’s eventual capture as well as the secret surveillance of Mumbai plotters that took place before and during the attacks. (We first reported some of the material in December with the New York Times.)
The Snowden documents show that, months before Mumbai, British intelligence began spying on the online communications of Zarrar Shah, a key plotter who was the technology chief for the Pakistani terror group Lashkar-e-Taiba.
Britain’s General Communications Headquarters, or GCHQ, had the ability to monitor many of Shah’s digital activities, including Web searches and emails, during weeks in which he did research on targets, handled reconnaissance data, and set up an internet phone system for the attack.
But based on documents and interviews, it appears that the British spy agency did not use its access to closely analyze data from Shah until a Lashkar attack squad invaded Mumbai on Nov. 26, 2008. Nor did the British tell the Americans they were watching Shah beforehand, despite the close alliance between GCHQ and the N.S.A.