The Shanghai Chest (1948)

Vic Armstrong arrives at his Uncle Judge Armstrong's home just in time to answer the telephone. Unknown to him, his uncle has just been murdered and the culprit is right there in the room with him! Phyllis Powers, on the other end of the line, recognizes Vic's voice, but just then Vic is knocked unconscious by the murderer. When he awakens, he (for reasons known only to movie mystery writers) pulls the knife out of his uncle's back, thus putting his fingerprints all over it, and just in time for the police, having been called by a worried Phyllis, to discover him standing over the body. Well, we know he didn't do it, but the police don't agree. Can Charlie Chan recognize the boy's innocence, and find the real murderer before Vic is sent into durance vile, or even worse?