"Shortly after, perhaps as soon as the light was extinguished, the murder must have been committed. The very presence of that light had been guardianship to the helpless old man below. When it was quenched, nothing remained astir, the way from without was open, the weapon stood only too ready to hand, the memorandum-book gave promise of booty and was secured, though nothing else was apparently touched. It was this very book that contained the signature that would have exonerated the prisoner. . . ."