Officers of the law frequently form a hasty conviction as to the guilt of a suspected person, and then distort all subsequent discoveries to conform to their established theory. The deplorable antecedents of Victor Danègre, habitual criminal, drunkard and rake, influenced the judge, and despite the fact that nothing new was discovered in corroboration of the early clues, his official opinion remained firm and unshaken. He closed his investigation, and, a few weeks later, the trial commenced. It proved to be slow and tedious. The judge was listless, and the public prosecutor presented the case in a careless manner. Under those circumstances, Danègre’s counsel had an easy task. He pointed out the defects and inconsistencies of the case for the prosecution, and argued that the evidence was quite insufficient to convict the accused. Who had made the key, the indispensable key without which Danègre, on leaving the apartment, could not have locked the door behind him? Who had ever seen such a key, and what had become of it? Who had seen the assassin’s knife, and where is it now?