[UltraViolence]

I doubt the Tor user was identified on the Tor network.

Most likely his Bitcoin donations gave him away, since Bitcoin is far from anonymous. He might also have left other clues such as an email address which he accessed from clearnet.

Anyway, it's pretty obvious LEA cannot identify Tor users en-masse. There have been several CP websites taken down which had hundreds of thousands of users, yet they only managed to arrest the website administrators. Only a handful of users were arrested, and mostly because of dumb mistakes.