Guess what happens if the FBI wins this, and Apple is forced to comply, and actually does decrypt this one phone, and probably later on hundreds or thousands of other iPhone 5 phones. Guess what: Apple will make the system so secure that this can never happen again.
This whole discussion has led me to reconsider the much too expensive iPhones, and my next phone might very well be an iPhone 6 or newer.
If your adversary is a well funded government agency you need to do a lot more than buy an iPhone.
If you're still alive when "they" want information they'll just extraordinarily rendition you and torture you. Or they'll implement laws like UK RIPA which require you to make available the unencrypted version when asked by a court. Or they'll install covert surveillance equipment.
This whole discussion has led me to reconsider the much too expensive iPhones, and my next phone might very well be an iPhone 6 or newer.