Bottom row, left side, look at the sharp points on the left, if that was a fatigue failure, those edges would have rubbed and gone flat, not look sharp. That is certainly a catastrophic failure, not a fatigue failure.
I have seen discoloration like that from OIL being introduced to a cracked area, and the rubbing together for a fatigue failure to look like that, but a tail section would not have oil introduced into that area! It is also vertical, any oils would have dripped down, I have only seen failures like this on stuff that was tested horizontally. (sloppy mechanics)
One other consideration, if I am all wrong, and that was a fatigue failure, (things happen!) this aircraft would have been showing serious control problems from vibration during flight, and most likely vibrate to a point that scared the life out of the passengers and crew or create a noise that would be clearly noticeable in flight.
I find it impossible that a failure like this would be caused by a fatigue failure that would not be noticeable in flight by any half trained air-crew, especially someone actually at the controls.
You got me on the bolts, though, I havent seen these in a while! I remember seeing NO BOLTs, but I might be thinking of the lower pictures, I can see the bolts in the top shot.
You mean, control problems such as several sharp, hard-over rudder movements?