Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

This collage here really tells it all. It's from the same day. On the left, it is definitely Jack Ruby. On the right, it is the shooter hovering in the dark with three detectives by the 3rd floor elevator shortly after the shooting.  

Note the broader nose on Ruby on the left. Look how much wider the base of his nose is than the bridge. On the right, the bottom of the man's nose is practically as narrow as the top.  He had a very narrow, pinched nose. Note the longer forehead on Ruby on the left, which has the effect of making his whole face longer. And look how much longer Ruby's neck is on the left. Look at the span between his chin and his shirt and compare it to the other guy. The guy on the right had a very short neck. The guy on the left had a much longer neck. The guy on the left was Jack Ruby. The guy on the right was NOT Jack Ruby. He was James Bookhout.