The FBI installed an informant in a mosque posing as a jahadist. The members of the mosque were so alarmed by this person that they reported him to the FBI.
I had always considered that we might have more to fear form our own government than from Islamic extremists as an abstract possibility, but I never really took it seriously before reading this. Makes me really wonder about the case against Mohamed Osman Mohamud too. This incident lends credence to the theory that Mohamud was entrapped. It would, apparently, not be the first time.