Further Foolishness:

The mystery had now reached its climax. First, the man had been undoubtedly murdered. Secondly, it was absolutely certain that no conceivable person had done it. It was therefore time to call in the great detective. He gave one searching glance at the corpse. In a moment he whipped out a microscope. "Ha! ha!" he said, as he picked a hair off the lapel of the dead man's coat. "The mystery is now solved." He held up the hair. "Listen," he said, "we have only to find the man who lost this hair and the criminal is in our hands." The inexorable chain of logic was complete. The detective set himself to the search. For four days and nights he moved, unobserved, through the streets of New York scanning closely every face he passed, looking for a man who had lost a hair.