It's actually the number of people arrested for committing crimes.
The troubling thing in cases like this is that even if the individual arrested wanted to commit a crime of this nature, he probably would not have been able to do so without help, and the only help he found was from the FBI. We don't know what he would have done had he not found that help. Would he have continued to fantasize and plan until he died of old age or until he eventually found that help, or would his mind eventually have changed and other, more pressing needs steered him away from this course?
I don't doubt that just about everyone, at some point in their lives, feels enough anger or depression to want to hurt a whole lot of people. Most of us, even those of us with a truly legitimate reason to be that angry, get over the feelings of wanting retribution. Has the FBI managed to uncover a 'plot' like this where there were more than two people involved that weren't FBI agents in it? So far in every case of this that I've read about, there was one or two people only, and the FBI provided just about everything and was involved in the 'planning'. We need to ask ourselves, are we catching criminals, or are we creating criminals of people that wouldn't have actually offended had they not been given access to materials and encouragement? I'm starting to lean towards the latter, and it may be time to consider laws that prohibit law enforcement from providing explosive materials or weapons, both fake and real, as 'support' to an individual or individuals that have not been able to acquire them on their own through other sources. It's one thing for the mole to give the would-be terrorist a fake detonator to use on the real explosives that the individual acquired, but it's another matter entirely to give them what they think is a thousand pound bomb as the entire basis for the criminal complaint when they probably couldn't have acquired it themselves anyway.