I doubt it took the FBI that long to track someone who was not trying to hide.
I don't have that much faith in the FBI. If anything, the ease with which they can gather as much data as they do would indicate that they just aren't very good at targeted objectives.
Now, I will make my own now. He did bounce his connection, and that is why they needed to use a trojan aimed at his account.
In which case he'd have the same results using Tor. And that takes a lot less skill.
Instead, if he had any competency he'd be using a cracked system so that any compromises would happen on the cracked system. And he'd use a command and control protocol that was different than the HTTP used to connect to Yahoo!.