A deadly blast that killed at least 37 people at the headquarters of Mexico's state-run oil giant "Pemex" was caused by a buildup of gas in the basement, an official said Monday. Mexican Attorney General Jesus Murillo Karam told reporters that no traces of explosives were found at the scene, according to a report of CNN. "The cause is clear; it's a gas explosion," he said, adding that the gas in question is believed to be methane.
