INDIANAPOLIS (AP) — Splintered beams and boards on a piece of charred earth were all that remained Sunday where at least two Indianapolis homes were leveled in a blast that killed two people and rendered homes for blocks uninhabitable.A backhoe raked through the rubble in the middle-class subdivision as clusters of firefighters and rescue workers weary from a long, chaotic day that began late the night before waited for their next assignment.The two-story, brick-faced homes on either side of those demolished by the blast were ruins. One home's roof was gone, a blackened husk left behind. On the other side of the gap, the side of a home was sheared off. Across the street, garage doors had buckled from the heat.It wasn't yet clear what caused the blast that shook the neighborhood at 11 p.m. Saturday. Residents described hearing a loud boom that blew out windows and collapsed ceilings. Some thought a plane had crashed or that it was an earthquake.Alex Pflanzer, who was asleep when the nearby homes were leveled, said he heard his wife screaming and thought someone was breaking in his house. Grabbing his gun, he checked the house and saw the front door was standing open."I walked outside and all the houses were on fire," he said.Pflanzer, his wife and two dogs were staying in a hotel room Sunday night. They were, however, without their cat, who refused to budge from the crawl space.Deputy Code Enforcement Director Adam Collins said as many as 31 homes were damaged so badly that they may have to be demolished. The explosion damaged a total of 80 homes, he said. He estimated the damage at $3.6 million.Some residents were allowed to return to their homes to retrieve a few belongings Sunday under police escort, officials said. Others whose homes weren't as badly damaged were allowed to go home, but officials said they would have to do without electricity overnight.Officials did not identify the two people who were killed. However, a candlelight vigil was held at Greenwood's Southwest Elementary School on Sunday night for second-grade teacher Jennifer Longworth. She and her husband, John Dion Longworth, lived at a home destroyed in the blast. WTHR-TV reported that friends, family and colleagues of the teacher gathered at the school.Deputy Fire Chief Kenny Bacon told reporters Sunday investigators haven't eliminated any possible causes for the blast. But U.S. Rep. Andre Carson, who represents the area, said he had been told a bomb or meth lab explosion had been ruled out.Bacon said the crisis could have been much worse. "I know we're very fortunate that some of the people weren't home," he said.Bryan and Trina McClellan were at home with their 23-year-old son, Eric, when the shock wave from the blast a block away shook their home. It knocked out the windows along one side of their house, and their first instinct was to check on their grandchildren, two toddlers who were in the basement. One held his ears and said, "Loud noise, loud noise."