VIDEO: Crews continued to comb through the rubble on N. Duke Street Thursday, looking for clues as to what might have sparked an explosion that killed one person and injured 25 others. Durham Fire Chief Bob Zoldos shed light on what happened in the moments before Wednesday's blast, but said learning what triggered the explosion could take some time. "It is truly a painstaking, very slow way of doing business, but it is necessary for us to get to the truth of that. It’s going to take a while for us to get to that conclusion," he said. On Thursday, crews brought search dogs to scour through the wreckage for anyone trapped, but the dogs didn't find anything, Zoldos said. They have now moved to a recovery operation.