in pitch darkness he knew his way in and out of basements , how to negotiate fire escapes , roofs and parking lots ; such was his knowledge of the void decks and of what routes a fleeing man might take that more than once , responding to an alarm from a man , mugger or purse snatcher , while other police rushed to the scene , roy raced through a back alley , vaulted a fence , and was standing , waiting in the shadows , for the thief to run into his arms .