Don't Bother to Knock (1952), directed by Roy Ward Baker.
Or: Don't Tell Mom the Babysitter is a Psycho!
This is a minor hotel-bound thriller only 76m long. Probably the only remarkable feature is the willingness to put a child in danger, which happened more often then than later. See: The Window (1949) and Rawhide (1951).
I review it for the talent involved:
Marilyn Monroe gets her first co-starring role at age 26. She did Clash by Night (1952) the same year and both films allow her more range than she would be allowed later. Here she is a mentally disturbed young woman, a danger to herself and others. We want her to be rescued somehow, before anything really bad happens.
Richard Widmark is still working his way out of psycho roles. Because of his early history we just presume he is a stalker or abusive boyfriend, but he turns out to be ok, if a little too eager for some action. He's a pilot; you know those flyboys.
Anne Bancroft is 21 in her film debut as a lounge singer and Widmark's love interest. She performs several songs and really was a singer, so maybe that is her voice. It sounds dubbed.
Elisha Cook Jr. and Jim Backus, both famous character actors and often playing roles where the character is not "all there".
Lucien Ballard photography.
I see the IMDB has "Other crew: Jerry Goldsmith, scoring tasks (uncredited)", his first mention in the database.
Available on Blu-ray from Twilight Time.