Neither Tor nor end-to-end encrypted messengers will cover the endpoints. It’s possible that they caught him using good old fashioned detective work. You don’t need a software back door for that.
Tor was created by NSA, half of Tor servers are run by NSA, not that secure
Tor was created by the NRL, which is a part of the US Navy and Marine Corps.
Tor was created by the Naval Research Labs, and was released to the public because it is secure.
The problem is that if it’s only the CIA or DIA using it, it’s easy figure out who is using it and where. Make it global and now there is a lot of noise to separate out.
Please don’t talk about child predators, and use the term “back door” in the same sentence. It ain’t right…