Mexico: gas leak caused state oil company blast

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An employee culls through debris searching for office documents amid the rubble left from an office building explosion, in Mexico City, Saturday, Feb. 2, 2013. A Thursday blast collapsed the lower floors of the Mexican state-owned oil company Petroleos Mexicanos, or Pemex, headquarters, crushing at least 33 people beneath tons of rubble and injuring 121. A Pemex spokesman said the floors hit by the explosion housed administrative offices. (AP Photo/Marco Ugarte)MEXICO CITY (AP) — A gas buildup ignited by an electrical spark or other heat source caused the blast that killed 37 people and wounded dozens of others last week at the state oil company's headquarters, Mexico's attorney general said.