Entertaining witty dialog, but ridiculous Agatha Christie story.
The movie itself is worth watching for Laughton and Lancaster along with other supporting actors and the amusing dialog. I personally do not get the appeal of Marlene Dietrich at all, with her silly lisp and overacting, but to each their own.
But the storyline is utterly illogical and ridiculous. If people think this is some brilliant crime story or courtroom drama, they're a bit slow.
First and foremost, no wife on the planet has EVER risked what would be YEARS of prison time for perjury during a capital crime trial. The Christine character must be portraying someone with a mental illness or something? She goes to such a huge extent to help her husband out, with massive personal sacrifice. There's a reason we've never heard of this "witness for the prosecution" technique ever working out in real life, no one would actually take the risk.
Next, she would have been IMMEDIATELY been put into custody, not allowed to wander around the court building and commit further actions in the courtroom after the trial! Who's idea was that? Utterly ridiculous.
Lastly, ALL legal evidence is SEALED in envelopes or other containers at all times to prevent contamination and to keep the trail of possession intact and it's always in the possession of court officials and immediately returned to storage. At NO POINT would a MURDER WEAPON just be allowed to lay on a table while the courtroom is basically empty! Again, ridiculous.
Sorry, but these and many other MASSIVE gaps in logic and reality of procedures simply makes the whole story a fantasy along the lines of the Wizard of OZ or the Hobbit. There's no basis in the real world to explain or allow the "creative" plot points that Christie throws into the story.