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I'm trying to find the title of this classic thriller movie. Can you help me?

In this film a widow owns and lives in a palatial mansion where her and her husband once lived before his death. He died in his laboratory in a fire or explosion which was once a part of their home. Along comes a man who seems to be well intentioned yet he's secretly evil deep down inside. The widow begins having nightmares that her dead husband is walking through her home, haunting her. These dreams are driving the widow to absolute madness and she thinks she is losing her mind. However it is the supposedly well intentioned man who has been posing as her dead husband for she isn't dreaming after all! She's having these horrible visions of her dead husband walking through their home while she's awake because this man is posing as him, made up to look like him after a fiery death. It isn't until the very end of the film she discovers the truth and the man is arrested. Can you please name the title, year of its release as well as the stars of this classic, lesser known thriller movie? Thank you.