"Who’s in the fragging stairwell?" Kyler Luppas demanded as he reloaded the Colt M-23 assault rifle while taking cover in the doorway on the eleventh floor of the Mariah Building. The plastiglass window at the end of the hall overlooked Ainsworth Street. He could see the red-and white-striped sawhorses blocking off the street and the gleam of the downtown advertising lights beyond.