“The Bureau has repeatedly said over the last six months that it has had more than 1,000 active probes related to the Islamic State. But, of these 1,000 or so suspected terrorists, the FBI only has the resources to thoroughly monitor a select few. The precise number of round-the-clock FBI surveillance teams is classified—and additional teams can be readied in an emergency—but sources familiar with Bureau resources say that the number is ‘shockingly’ low, only in the dozens. At one point last year, sources reported that the Bureau was watching 48 people intensely, a number that is towards the upper limit of the FBI’s regular surveillance resources.”
Source: The FBI’s Growing Surveillance Gap – POLITICO Magazine