Why did Benson commit murder?
It was never adequately explained in the movie. Did the novel explain?
Show me the holes!
Benson failed a mental stability test and was being replaced on the mission by the guy he killed. He fushed the other guy out the airlock and took his place because he still wanted to go on the mission.
What isn't quite clear to me is why Benson so desperately wanted to go on this mission. Eventually what he would have done would have been found out.