In agreement with the other comment, this is a superior episode of AHP. Simply and perfectly titled, "The Motive" has so much in it that it seems longer than it is, but in a good way because it's so interesting.
The plot setup, while preposterous, is well handled and convincing. And the actors are well cast, giving energetic performances. Skip Homeier (Tommy) never achieved real stardom, but he made an impression every time he appeared on screen, in films such as "The Gunfighter" (where he plays a young gunslinger lacking common sense) and especially in "Tomorrow the World!" (in which he plays a former Hitler Youth, with chilling realism). TV stalwarts William Redfield and Carl Betz (soon to play Donna Reed's husband on her sitcom) bring plenty of life to their characters, and we even get Gary Clarke as a bellboy for one scene.
What makes this episode so memorable is the well-played, cold calculation of the characters, and the brilliant twist ending, which wraps things up, yet leaves the viewer thinking. "The Motive" is a like a good short story come to life. Is Rose Simon Kohn's original story comparable? It may be worth seeking out.