Discussion of "The Dark Mirror"
Details
Identical twin sisters Ruth and Terry Collins (de Havilland in a dual role) are almost impossible to tell apart. After Terry visits the apartment of Dr. Frank Peralta, he is found stabbed to death. Detective Lt. Stevenson (Mitchell) suspects Terry, but she has witnesses that can vouch for her whereabouts the evening of the murder. When Stevenson discovers that Terry has an identical twin sister Ruth, identifying the murderous sister becomes more complicated.
For some background on the film click the link below.
https://classicmovieman.blogspot.com/2020/11/olivia-de-havilland-stars-as-identical.html
To watch the film on YouTube click the link below.