I don't get it; why has he only arrested 86 then? Shouldn't he be nabbing all 7000?
It is not worth the time, effort or money to nab a person who has only downloaded a picture or two. The best they could get is a charge of "viewing" and that is iffy at best.
They got the ones they wanted, the ones that were preying on children, taking pictures of them, luring them in, molesting them, etc.
Of the other 6900, probably a good 90-95% were scared off of any sites they register to just by the sting being made public. That alone was all the FBI probably was hoping for in those cases.