In Jim Garrison's book (one of the two books that Oliver Stone based his movie on), there are official autopsy photos. In one photo with JFK's head towards the camera, any person can see a metal rod of some type dead center in JFK's head. Why would that metal rod be there? To hold up the skull together? Also, I clipped out a small article in '92 where the Russians who had Oswald under surveillance came out and stated that Oswald was a lousy shot with a gun since the Russian intel observed him at a shooting range.
Without seeing the picture it sounds like you're describing a tool commonly used during autopsies to chart a bullet's trajectory through the body.