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Fire and smoke rise at an upscale shopping district in Kansas City, Mo., where a city official said a gas explosion sparked a block-engulfing blaze, Tuesday evening, Feb. 19, 2013. (AP Photo/The Kansas City Star, Keith Myers) KANSAS CITY OUT

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.