"Alfred Hitchcock Presents" My Brother, Richard (1957)

Martin Ross is a district attorney with a fighting chance at his party's nomination for governor. But Martin's brother, Richard, wants him to have more than a fighting chance. So, as the other candidate takes a shower at his country club, Richard walks in with a gun and a silencer and walks out with one less bullet. The sheriff calls Martin and tells him the news of the murder. Later, he has a suspect: the victim's teenage caddy. But Martin already knows his brother is the real murderer. And Richard takes Martin's wife hostage to ensure than no one else finds out.