In post 10, there is a link to a military photo forum with this post:
Reports of USAF KC-135 crashing near Bishkek, Kyrgyzstan
If you look closely, the fuel tank cap is missing with a fuel stain around the hole. When the tank cap is correctly installed, the cap locks into place and is impossible to remove unless you intend to do so. The locking lugs appear to be undamaged. I wonder if a cap wasn't installed correctly.
RIP to the crew.