Howdy.
As most Americans know, this year will mark the 50th anniversary of the execution of Lee Harvey Oswald by electric chair for the murders of President John F. Kennedy and Dallas police officer J.D. Tippit. The evidence was pretty strong (especially in Tippit's murder), in spite of attempts to knock holes in it throughout the years; Errol Morris made a good case for his guilt in his Oscar-winning documentary Texas vs. Oswald.
So, here's a WI: WI Oswald was somehow killed before his 1964 trial? Suppose someone manages to shoot him while he was being escorted from jail to jail a couple of days after his arrest.
One possible effect: the conspiracy theories will become more widespread than OTL, especially without a trial...