Back in the mid 70's I was watching a late-night scary show called Shock Theater. Every Saturday night they played old horror movies. One night I saw bits and pieces of this black and white movie that had to have been made in the 40's.
It seems like the plot took place during or after World War I. I remember seeing biplanes in the movie. A guy (Man One) begins the plot by sitting in a room and speaking to another man. Man One has a bag with him. The rest of the movie is mostly a flashback to what has already happened. At the end of the movie it returns to the two guys talking and Man One opens the bag and reveals a human head inside it. Not much in the way of horror since it was mostly a thriller instead. I gathered that Man One had some issue with the dead guy throughout the movie and ended up killing him and removing his head.
Which movie was this?