LOUISVILLE, Colo.—Search teams looked for two missing people on Sunday in the snow-covered but still smoldering debris from a massive Colorado wildfire, while people who barely escaped the flames sorted through what was left after the blaze and investigators tried to determine its cause. The flames ripped through at least 9.4 square miles and left nearly 1,000 homes and other buildings destroyed in suburbs between Denver and Boulder. It came unusually late in the year following an extremely dry fall and amid a winter nearly devoid of snow. Experts say those conditions, along with high winds, helped the fire spread. In hard-hit Louisville, Susan Hill walked her dog in the well-below freezing chill Sunday morning down a snowy street. She choked up as she remembered three days ago seeing the sky change color from the hill where she used to watch fireworks—and then the nervous sprint out of town with …