The Dark Mirror

In The Dark Mirror (1946), directed by Robert Siodmak (The Killers), a man is murdered and there's an obvious suspect, but she has an identical twin sister (both played by Olivia de Havilland, Gone with the Wind), and one of them has a cast-iron alibi. The perfect crime? A psychologist with a specialist interest in twin psychology delves into the heart of the mystery, at considerable risk to himself.