The FBI’s defenders say investigators would, at any one time, have been monitoring hundreds, possibly thousands of exchanges between Awlaki and interlocutors in the U.S. Many of them would be disaffected young men, expressing rage against the West and support for the activities of jihadis everywhere. Then along comes this communication from a senior military officer. It’s innocuous, and well within the scope of the officer’s legitimate area of interest and research. Rather than raise any alarm, say intelligence officials, the communications from Hasan would have seemed “safe” and been put aside, while FBI monitors to focused on Awlaki’s other, potentially more worrisome correspondents on these shores.

Says Juan Carlos Zarate, who was President George W. Bush’s Deputy National Security Adviser for combating terrorism, “Given the cover [Hasan] used, as someone researching the effects on Muslim soldiers of operating in Muslim countries [his approaching Awlaki] was not wholly illegitimate. It doesn’t raise the specter of dangerous or criminal activity.” In those circumstances, the officials monitoring the communications between the psychiatrist and the imam might reasonably assume Major Hasan was doing “legitimate research, on behalf of the U.S. military,” he adds.