From RKO Mystery Files

Bonita Granville/Morgan Conway Discover The Truth About Murder (1946)

An intriguing title, whatever "truth" there is about murder not necessarily presented here, but humbling for my mis-guessing the killer in a first half. Bonita Granville would rather prosecute crimes for D.A. Morgan Conway than marry him --- she'll learn! Lew Landers directs ... did you think we'd ever see a day when TCM would run a twelve-hour festival of his B's? I say nothing's impossible in a wake of that. What with Granville and Conway, you could call this Nancy Drew meets Dick Tracy, which is most of what gives it appeal. Cute trick Granville married well and was made rich by a dog (Lassie). At least it rescued her from doggie movies like this. Conway had a neat voice and I actually like him better as Tracy than Ralph Byrd (is that sacrilege?). RKO did these by bushels, so surely someone was watching. Just checked the IMDB and commenters all said they knew the killer right away, which really makes me feel like an idiot.