Philo Vance
It wasn't really so difficult. Remember, the man who committed this particular crime must have had certain definite qualities—a mind capable of working out a well-planned and brilliant course of action, willing to take a desperate chance and see it through.
Now, consider the men in the game. Jimmie I ruled out at the start. But I've known him as a boy, and his youth and impulsiveness were hardly consistent with such a...such an obviously premeditated murder. Lindquist was far too excitable and erratic to have plotted such a carefully calculated crime. Cleaver, much too cautious, and entirely lacking in the necessary boldness. Mannix, timid and unwilling to take any risk except upon an absolutely sure thing.
The only man at the table with enough imagination to plan such a crime, and with sufficient self-confidence and daring to carry it through, was Spottswoode. When he held a pair of deuces, refused to draw to them, and bet every chip he had on the chance of bluffing me out, a realization suddenly dawned upon me that he was the murderer, for he was the one man of them all psychologically fitted for such an act.