Mitchell Beaupre’s review published on Letterboxd :
Being based on an Agatha Christie play, I should have known going into Witness for the Prosecution that I was in for some shocking twists and turns. Nothing, though, could have prepared me for what I was about to experience. It's hard to talk about the film without going into its final act, but I'll avoid spoilers and be relatively vague in singing its praises to the high heavens. Billy Wilder directs the picture with his usual energy that makes it constantly enjoyable, but one of the finer aspects of it comes from the ways that his script (co-written with Hary Kurnitz) makes alterations from Christie's source material that make it as much a work of his as it is hers.
Those impeccable plot turns are all Christie, but Wilder and Kurnitz also do what they can to add some fine humor to the picture. They shift the perspective from Leonard Vole, a man on trial for the murder of a widow, to Sir Wilfrid Robarts, the famous and poor of health man who has agreed to defend him. Robarts is played by Charles Laughton with a wealth of spirit that is a perfect match for Wilder's charisma, and the writers also added the character of Miss Plimsoll (played by Elsa Lanchester) as Robarts' caretaker. Laughton and Lanchester bounce off each other so well, creating a charming antagonism that is a nice contrast for the grim nature of the case he takes on.
Vole, played by the great Tyrone Power, insists on his innocence and is constantly at a breaking point while hearing witness after witness stand up and bring him closer to his imprisonment and his only alibi is in the form of his wife Christine, brought to the screen by Marlene Dietrich. To reveal more would hurt the astonishing twists in the narrative, but Christine is the key factor in this case and the way it turns through me for one loop after the next.
My one complaint with the film is the use of flashbacks in earlier scenes with Vole describing the details of his relationships to Robarts, particularly one with Christine that was designed entirely to get an image of Dietrich's legs on screen, but those are over and done quickly and when the film is over there isn't much that can take away from the power of that final act. I found myself slightly disappointed during the middle section of the film by how conventional it had been playing out so far, but I should have known better than to doubt the build-up power of Christie and Wilder.
Wilder has always been one to deliver truly memorable endings in his pictures, and Witness for the Prosecution builds to a final act that it just one twist after the next, all of them leaving me stunned. The performances excel, with Laughton's charm, Power's desperation and Dietrich's cold and terrifying power, and they all get even more impressive as the truth comes to the surface in one gut punch after another. Witness for the Prosecution is a brilliant film not because it pulls the wool over the eyes of the audience (which it does), but because it pulls it over the characters as well.
Films that rely on their twists makes the mistake of building everything specifically for the audience, but here these turns are just as surprising for the characters as they are for those watching it. These revelations are shocking in a narrative sense but also in what they mean for the characters, and that's what makes them, and the film itself, truly stunning.