An Act of Murder (1948)

A principled but stubborn judge, Calvin Cooke, 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.

Cooke is unaware that his daughter Ellie and the lawyer are romantically involved. Ellie complains about how unyielding her father can be to her mother, Cathy, who is preparing to celebrate her 20th wedding anniversary.

Dizzy spells lead Cathy to see Dr. Morrison, the family physician. Tests later prove that her condition is fatal, but rather than inform the patient, the doctor confides in Cooke, who decides to keep the information secret from both wife and daughter.

The judge takes Cathy on a second honeymoon. Her condition worsens, including excruciatingly painful headaches. Cooke gives her toxic pain-relief pills provided by the doctor, lying that they are aspirin. Cathy, however, accidentally discovers the doctor's written diagnosis and demands they return home.

In the car, her pain becomes unbearable. Cooke can stand it no more. He deliberately drives the car over an embankment, not caring if he is also killed in the crash. He survives and confesses that he caused the wreck on purpose.

Douglas agrees to defend the judge against criminal charges, at Ellie's request. He is able to prove that Cathy was already dead from the pain pills before the crash, while the judge, still feeling guilty, now understands better how critical to a case a defendant's state of mind can be.