It was the shell that was never found. Had to have been. Because I don't believe that any of the four shells that were recovered were split. BTW, those four shells were matched to Oswald's revolver to the exclusion of all other weapons. Oswald shot Tippit. It's a historical fact.
It's a historical fact. For many years it was a "historical fact" that Marinus van der Lubbe burned down the Reichstag building in Berlin in 1933. Van der Lubbe was convicted for it and executed in 1934. It took until 2007 to prove the "historical fact" wrong.
For centuries the Donation of Constantine was considered a "historical fact" until it was proven to be a forgery
So much for "historical facts"