Witness for the Prosecution is a 1957 American legal mystery thriller film directed by Billy Wilder and starring Tyrone Power, Marlene Dietrich, Charles Laughton, and Elsa Lanchester.

[2] In the film, a man accused of killing a wealthy widow who had named him as the main beneficiary in her will undergoes a trial during which his wife testifies against him.

Vole is accused of murdering Emily French, a wealthy, childless widow who had fallen in love with him and named him as the main beneficiary in her will.

When Sir Wilfrid speaks with Vole's German wife Christine, he finds her cold and self-possessed, but she does provide an alibi, although it is not entirely convincing.

During the trial in the Old Bailey, the Crown introduces testimony that Mrs. French had seen Vole with a younger woman and planned to confront him, but Sir Wilfrid believes his client to be innocent.

While a wife cannot be compelled to testify against her husband, it is revealed in court that her marriage to Vole is invalid, as she was already married to another man, Otto Helm, who is still alive and living in Germany.

She explains that she had gone through a ceremony of marriage with Leonard, a Royal Air Force officer serving in Berlin's British occupation zone, solely to escape from Soviet-controlled territory to the West.

Now fearing that his client must inevitably be convicted and sentenced to hang, Sir Wilfrid is unexpectedly and fortuitously contacted by a woman who offers to sell him letters written by Christine to a lover named Max.

Sir Wilfrid is troubled, and his worries prove justified when Christine, brought into the courtroom for safety after being assailed by the departing crowd, tells him what she had done to secure the acquittal.

As she is arrested, Sir Wilfrid decides to further delay his retirement to serve as Christine Vole's defence counsel, stating that what she did was to execute Leonard.

[3] In a flashback showing how Leonard and Christine first meet in a German nightclub, she is wearing her trademark trousers, made famous by Dietrich in director Josef von Sternberg’s film Morocco (1930).

[14] In TV Guide's review of the film, it received four and a half stars out of five, the writer saying that "Witness for the Prosecution is a witty, terse adaptation of the Agatha Christie hit play brought to the screen with ingenuity and vitality by Billy Wilder.