Son of Ingagi (1940)

A wealthy old recluse wills her fortune and exceedingly-gloomy house to a pair of newlyweds, Robert and Eleanor Lindsay. Years before, Dr. Jackson had been in love with Eleanor's father, who was younger than her and did not return her love. N'Gina, an ape-man, Dr. Jackson brought back from Africa drinks a potion she had concocted in her laboratory, for a specific reason, but N'Gina turns on her and kills her, which is not what she had planned. Then he murders her attorney, Bradshaw, who is hunting for $20,000 in gold she had hidden in her gloomy house. Her brother, Zeno, an ex-convict, finds the gold but N'Gina isn't bothered by the bullets Zeno fires at him and kills him also. Detective Nelson then goes looking for it.