Writing for The Verge, Russell Brandom has penned an excellent look at the differences between the FBI's job and the tasks set for the NSA and CIA, and how those differences put the two camps at odds over Apple and iPhone encryption. It's excellent piece, and if you are following the fight between the FBI and Apple, I recommend it in full.
Check It Out: The Verge Explores 'Why the NSA is staying out of Apple's fight with the FBI'