An Act of Murder is a 1948 American film noir directed by Michael Gordon and starring Fredric March, Edmond O'Brien, Florence Eldridge and Geraldine Brooks.

[4] Calvin Cooke, a principled but stubborn judge, presides over a murder case in which lawyer David Douglas is unsuccessful in proving that his client's state of mind was a mitigating factor.

At the party, Cathy talks to Dr. Morrison, an expert neurologist and friend of the family, about her intermittent symptoms of weakness and headaches.

The doctor gives him a bottle of pills called Demarine for pain relief, strongly warning him about the maximum dosage, and a prescription for more.

While he is calling the doctor from a pay phone so Cathy will not hear, a dog is run over in the street, and a police officer ends its suffering with a gunshot.

Cooke agrees, and announces that in expiation, if allowed to remain a judge, he will now rule on the basis that similarly a person can be legally guilty but morally innocent—just what Douglas and Ellie have been asking for.

The Courthouse Square set (which later received that name for having been prominently featured in Back to the Future) was built on the Universal Studios backlot for this film.