Conspiracies from the 1940s

Part of my story is set in the 1940s and I was thinking of tying it into a conspiracy or unexplained event from that time period. I know about the Roswell Incident and the disappearance of Flight 19. Anything else I could use?

The disappearance of Glenn Miller.

This is probably earlier than you want, but there's the "Business Plot" of 1933, which was a suspected plot by conservative businessmen in collusion with veteran's organizations to oust FDR. There was a senate hearing, but no one was ever prosecuted.