India, May 4 -- The building at B-13, Vivek Vihar Phase-I, does not look like a site of catastrophe from the front lane on Sunday morning. The facade is largely intact. It is only when you walk around to the rear, past the narrow passage that fire trucks could not enter, that the full picture presents itself: blackened window frames, hollowed-out rooms, balconies stripped of the grilles that once sealed them shut, and the smell of smoke that has soaked into the brick and will not leave.

Nine died here before dawn Sunday: three families, three floors, one building, including a toddler. A resident, here for four decades, watched from his first-floor balcony around 3:30 am. At first, he saw a flicker on the second floor of the next building...