The FBI found out his bank account information from buying ads. He probably bought something on iTunes and that would be sufficient for Apple to be given a search warrant for any data related to x IP address, billing info, email address, or name. Any identifying details they collected at that point.
Not hard to connect the pieces once you have a money trail. That's an investigative gold mine.
Not hard to connect the pieces once you have a money trail. That's an investigative gold mine.