What enables pudd'nhead to crack the case

Tom feels so confident that he has escaped all liability that he decides to stop by Pudd'nhead Wilson's house that night to tease him about it. He finds Wilson in his house, still pouring over his glass slides, trying to match the knife prints to the fingerprints of some town woman. Tom notices a slide with Roxy's name marked on it, and picks it up to take a better look. In doing so, he inadvertently leaves his own fingerprint on the glass. When Wilson sees the print, he immediately recognizes it as the print from the knife. He chastises himself for not considering that the mysterious girl might be a man disguised in girls' clothing. After Tom leaves, Wilson takes out and examines the various fingerprints he collected from Tom over the years. This leaves him perplexed, as Tom's baby prints do not match his later records. Wilson goes to bed still confused, but when he awakes from a dream, the puzzle is solved.