Then the FBI paid a hacker who broke into it.
It is not hard. Clone the hard drive on the phone, then start a brute force hack on the clone. After 10 tries, the clone self-destructs. Rinse and repeat. Most phones are only secured with a 4 digit locking code, so it is not a big deal.
The Key is not that simple, nor is it on the hard drive. The passcode only unlocks the AES encryption key, and is used to build part of the Encryption Key each time it is entered in a SECURE PART OF THE IOD DEVICE. So, Flick, passcode is only a portion of the encryption key, and even then it is the only the one-way HASH of the passcode which is calculated in a secure part of the iPhone that is then used as part of the key, entangled by an algorithm in the rest of the key. . . and that KEY is NOT four digits but can be larger than 144 characters in size.
It's a 256 bit AES encryption. . .and Apple allows up to 256 characters for the passcode and you can use every single one of the 223 characters on the virtual keyboard in your passcode. Such a brute force, try every key method of trying to break a 256 bit AES encryption can, and most likely will, take longer than the Universe has to yet to live. See my post above about the calculations using just a 16 character passcode.