Interesting point. AFAIK they requested the key to decrypt previous communications. From security point of view, his move makes perfect sense. If FBI wanted to decrypt future communications, they would probably have specified that in their request. Then he would indeed break court order and could be hold responsible.
On the other hand, it would be hard to prove any actual obstruction, since the service was shut down and all users notified about this whole situation.
On the other hand, it would be hard to prove any actual obstruction, since the service was shut down and all users notified about this whole situation.