Well, I wouldnt say that we have no clue what the weapon was; the weapon was something like the flashlight (golf club, baton, bat, etc).AK,
Here is some further information for discussion:
Force required to cause a depressed fracture in JonBenets skull in the posteroparietal region:
Modern studies of skull fractures conducted by the American military demonstrate that it takes a minimum of 90 foot-pounds delivered over 1 square inch to fracture the human skull with a blow delivered to the front of the head. If the blow is delivered to the temporal/parietal area, 45 foot-pounds will produce a fracture. A blow to the zygomatic region, the bony arch on either side of the face below and around the eye, requires only 18 foot-pounds of force to produce a fracture. A mace weighing 1.8 pounds can be swung at a speed of 60 feet per second by the human arm so as to generate 101 foot-pounds of energy on impact, more than enough to fracture a human skull at its strongest point.
From Sumer to Rome: The Military Capabilities of Ancient Armies,Richard A. Gabriel, Karen S. Metz, page 57
FFJ has an excellent link with photos and diagrams as well (page 16 was my reference above):
At six years old Jonbenets skull should have been closer to an adults then an infants by some degree!
The strength of bone isnt effected by relative position between object and target, and, I dont think this target could have moved fast enough in any direction to noticeably effect the force required by the striking object to cause this damage. So, the force required to fragment bone remains pretty much the same.
As for position between Jonbenet and her killer, the injury suggests that they were probably front to back with the killer striking from overhead and behind. She could have been standing, sitting or lying down; he could have been standing or sitting on top of her.