The bottom bolt is swivelled up. Two different keys are used.
I don't see how the locks work unless a pin is inserted through the front and the lock is a cam, that engages the far side of the pin.
http://ladybranwick.deviantart.com/art/ ... k-80034846
If you look at the bottom of door jam you'll see both sides of the door as they fit in the recess. The recess appears to be over an inch and a quarter deep. The other front boards are probably as thick. If the lock is on the back of the door, unprotected, then a prisoner could activate it from there BUT if the lock was sandwiched between two boards the prisoner couldn't touch it.
Since there is a opening at the bottom of the door, I assume that a food tray would be slid underneath. That probably means there are no eyelets in the walls which a prisoner is chained to otherwise they couldn't pick-up the food.
So, if the lock is sandwiched between two thick boards, it's reasonable to assume the thickness of the door is at least 4.25 thick (108 mm). ALSO, The number of rivets suggests that there is more then one layer of wood. Notice how the rivets DO NOT extend to the sides of the door but are located in the center. IF there were three or four metal straps that ran across the wood, on the back side, then the rivets would be in a horizontal line. That's not the case. There must be three layers of wood because - in those days - wood was not cut to standard sizes. Because there are different widths of wood on that door it was necessary to use a number of rivets One of the reasons there are over 180 rivets is for decoration purposes, A second reason is to hold the parts together seeing as they didn't have a good glue and the third was to confuse people as to how the door is constructed so thy didn't know the weak points.
Do you have another theory other than you don't think Mark is an expert? I would like to read your hypotheses,
Thank you