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Utility workers repair gas lines near a building that exploded and caught fire in the Plaza shopping district of Kansas City, Mo., Tuesday, Feb. 19, 2013. (AP Photo/Orlin Wagner)

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.