This is potentially more dangerous than Apple creating something for use. Everyone is worried that if Apple did create a forked version of their OS to comply, it would compromise security for everyone - without question. Now - it MAY be possible for someone who has less corporate responsibility to create a way into a locked phone. This should be more disconcerting than Apple helping. I sincerely hope it winds up being impossible for a 3rd party to hack in.
You're making one fundamentally untenable assumption: that law enforcement, especially at the federal level, isn't populated by lying fascists.
I find it far more likely that either the phone has long since been opened or they know there's nothing of value on it and they aren't going to try.