Dana Andrews has a deep inscrutability; look at him and you see a handsome charmer with dark secrets and skilled at hiding at them. Decades later, we saw this persona in Mad Men's Don Draper, played by Jon Hamm. The two men even look alike. All of which make the nifty plot twists in Beyond a Reasonable Doubt plausible. Director Fritz Lang brought an experienced hand to the genre. Noir nuggets are sprinkled throughout the film, which is basically a tight police procedural drama. Sidney Blackmer as the newspaper publisher brings idealism with an undercurrent of menace. Twelve years later, Blackmer would delight and frighten audiences playing a Satanist in Rosemary's Baby.
I would have loved to have seen more of Joan Fontaine. There's a "been there done that" to her role as the deceived, loyal wife/ fiancé. But even Joan Fontaine in small doses is great. The ending in Beyond a Reasonable Doubt was in keeping with the Production Code. But absent the Code, I could see Joan pulling it off in not turning in her boyfriend, even accepting what Andrews did as a necessary and just means of getting out of a jam.
I love your comments on Dana Andrews - he does seem to be "unreadable".