Clearly the perp was a fathead,and sounds like the intended victim fired back with standard ball ammo, metal jacketed, so it did not deform. A better round would have expanded and emptied out anything serious between that spot and the fresh air on the other side of his head.
A glancing shot could well have deflected off the hard bone of the forehead, but I am mystified as to why it would be spent so quickly and just stay there.
It happens in hunting situations where a hunter tries to shoot a deer (or worse, a bear) between the eyes and the bullet skips off the top of the head into the woods leaving a very nervous deer or annoyed bear to confront.
I have no further explanation why it did not penetrate any further, except would throw away the rest of that box of ammo and buy better stuff.
Meanwhile, darned if I can see a real privacy issue here :-) The perp is withholding evidence in a criminal case. If Bubba Clinton could be obliged to offer a DNA sample to compare to residues on the blue dress, this little thug should get his forehead fat emptied. (Since when do teen gang members have access to fancy civil rights lawyers?)