Moment of Indiscretion (1958)
At first this is a murder mystery on the surface, and by the last half it's a murder mystery deep down. And hence it loses its earlier distinction as a tale of indiscretion. Janet Miller is played by Lana Morris, a very British part of a British cast in this British whodunnit, and Janet has witnessed a murder. But she was at the scene of the crime (and totally innocent) because of a small interlude (also quite innocent) with her former boyfriend. Her current husband, played by equally British Ronald Howard, can't find out.
But of course he does, and dramatically, while the police are questioning her. His initial unquestioning defense of her, and their later joint struggle for trust and renewal, is the best and most original part of the movie.
I emphasize the Britishness only because this has little resemblance to an American crime film. It's not a noir at all, lacking both the gloom of the characters and the gloom of the photography. And it has the classic drawing room fascination with assembling clues and solving the crime through simple observation and conversation. Guns only show up at the very end.
I actually liked this little movie for the indiscretion, the human drama, enough to like the movie overall. If it's not an intensely satisfying crime movie, thriller, or interpersonal drama all in all, it is still well made and well acted, with convincing detectives and protagonists. Never mind the killer and his girl, who are caricatures of some kind (probably taken from some earlier American noir).