The Six Napoleons
'Now, you see how the affair begins to clear up. The other fellow is probably an Italian also, and a member of the Mafia. He has broken the rules in some fashion. Pietro is set upon his track. Probably the photograph we found in his pocket is the man himself, so that he does not knife the wrong person. He dogs the fellow, he sees him enter a house, he waits outside for him, and in the scuffle he receives his own death-wound. How is that, Mr. Sherlock Holmes?'
Holmes clapped his hands approvingly.