Danger on the Air (1938)

Caesar Kluck, soft-drink magnate, is found dead in the office of a big radio-broadcasting company. Benjamin Franklin Butts, a sound engineer, discovers that Kluck met his death from cyanogen gas, administered in some mysterious fashion. Harry Jones, head of the company, fires Butts for making the murder public. Kluck has made many enemies and there are numerous suspects, including Christina "Steenie" MacCorkle, who is in love with Butts; her brother Alexander; radio announcer Dave Chapman; Tony Lisotti, the janitor who had discovered that Kluck was making love to his daughter Maria; Kluck's physician, Doctor Leonard Sylvester; and Joe Carney, a racketeer who had been doing Kluck's dirty work. Butts pursues his investigation and his only clue is a deflated toy-advertising balloon he has found next to Kluck's body. Later, Butts discovers Tony's body in a broom closet and, nearby, finds another deflated balloon, a straw and a pin. He then calls all the suspects together...and solves the mystery.