If you read the letter, they already said they have, do and will aid law enforcement in any lawful way they are able.
They question the lawfulness of this particular request.
They question the lawfulness of this particular request.
But, one thing has been bugging me about this case and your comment that Apple questions the "lawfulness of this particular request" leads me to ask:
Does 4th Amendment protection end at death...?...the terrorist is obviously dead...
I've been looking and don't find answers that satisfy me...?
Anyone?
So this request is really a request for Apple to develop a way to break their own encryption, which brings up a lot of slippery slope concerns. If Apple can be forced by the government to develop a way to break into this version of their OS, what would stop them from being forced to develop cracks for other versions of their OS?