The Web (1947)

Leopold Kroner, formerly of Colby Enterprises, is released after five years in prison for embezzlement. Andrew Colby, claiming that Kroner has threatened him, hires lawyer Bob Regan as a secret bodyguard. Sure enough, Kroner turns up in Colby's room with a gun, and Regan kills him. Then Regan, who sticks around to romance Colby's secretary Noel, begins to suspect he's been used.