"MEXICO CITY -- A gas buildup under a building in the headquarters of Mexico's state oil company caused a blast that killed 37 people and wounded dozens, the attorney-general said Monday, ending days of near-total silence by authorities about the petroleum giant's worst disaster in more than a decade."

"Attorney-General Jesus Murillo Karam said an investigation by Mexican, Spanish, U.S. and British experts found no evidence of explosives in the blast that collapsed several lower floors of the Petroleos Mexicanos administrative building on Thursday afternoon. He said investigators believed that an electrical spark or other source of heat had detonated the gas.

With the exception of three victims, none of those killed had the burn marks or damaged ear drums that are typical evidence of a bombing, he said. Nor was there any sign of a crater or fracturing of the building's steel beams, also common signs of the detonation of an explosive device."

Michael Weissenstein reports for the Associated Press February 5, 2013. [2]