Devils Advocate here: Anonymous or someone else who wanted to get rid of some potentially incrimminating evidence of high ranking people? If Anon can find the sites then I'm sure FBI knows them. Sure rid the content but save the text and usernames...

Edit: It seems CIA has had a key position in tor at some point. By applying for a job at tor. https://www.reddit.com/r/TOR/comments/4pw7bz/tor_infiltrated_by_cia_agent/

FBI has only tried to infiltrate tor by owning a lot of nodes and controlling it by mass. Entry and exit nodes. https://security.stackexchange.com/questions/119146/tor-cracked-how-do-you-think-the-fbi-did-it

So basically CIA owns the network and FBI tried to take it over? Dont know if this is still the case, but why would anyone give it up?