We've made some arrests. But I'm guessing out of those 5000, a good percentage are deemed to be non threats and dropped. And of the remaining percentage, it's more valuable to keep tabs on them unless they are planning something imminent. Catch the big fish that way.
Of course with the publicity due to the stinking leakers, it probably scuttled a bunch of leads.
Yes, that was sarcasm. Except for those folks who really believe that someone could do any significant damage to the Brooklyn Bridge with an acetylene torch, without being REALLY obvious for a REALLY long time.