One thing that I don't think has been covered enough in this whole debate about forcing Apple to unlock the iPhone is that "Farook and his wife destroyed their personal iPhones, and the hard drive from their computer was removed and has never been found"[1]. The iPhone the FBI is after is one that was issued to him by his employer. It seems to me to be very unlikely that Farook and his wife would go to the trouble to destroy all their other electronics but somehow forget to destroy his work phone (assuming his work phone had incriminating information on it in the first place).
[1]: http://www.usatoday.com/story/opinion/2016/02/18/apple-court...