If I Should Die Before I Wake (1952)

The plot centers on Lucio Santana, a lovable prankster and class clown whose dad happens to be a detective working on the serial killings of local children. When Lucho makes friends with a girl in his class, she divulges to him that a man who lives in the woods near the park has been giving her free lollipops, and plans to take her to his candy house. But she makes Lucho vow never to tell anyone. When the girl winds up murdered, Lucho is torn between honoring his word to his slain friend, or telling his father that he knows who the man is.