The standard playbook for rolling up criminal conspiracies is to arrest a low level member, offer him a reduced sentence in return for testimony, arrest the next guy higher up based on that testimony, etc. (The only way to prevent that would be a fully trustless "cell" structure where none of conspirators know each other, which has never been done in real life.)
You will notice none of this requires communications intercepts. This is because the feds are simply lying when they say encryption prevents law enforcement operations.