Inner Sanctum Mysteries.  Episode 56, Skeleton Bay.  A lady novelist witnesses a murder and, in a surprise plot twist, decides to help the murderer dispose of the body.  (February 5, 1946)

Crime Classics.  Episode 16, The Alsop Family, How It Diminished and Grew Again.  This episode finds a lonely figure atop a hill, digging a grave.  He figures about an hour to finish it, plus another hour to go and murder the person who he will bury in it.  (August 24, 1953)  Note, Bart, episode 15 is the same program but with very lousy quality.  Episode 16 sounds way better.