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An ATF agent and other investigators look down a hole in an alley near JJ's restaurant after an explosion and fire tore through the establishment Tuesday evening near the Country Club Plaza Wednesday, Feb. 20, 2013, in Kansas City, Mo. The fire killed one person and injuring over a dozen. (AP Photo/Ed Zurga)

Kansas City gas explosion

A day after a natural gas explosion

leveled a popular restaurant, investigators raced to search the rubble

and tried to understand how the blast happened despite suspicions that

flammable fuel had been leaking, maybe for weeks, somewhere in the busy

outdoor shopping area.