UPDATED 19:24 PM EST, February 5, 2013
Mexico's attorney general said Monday night that a buildup of an unspecified gas was responsible for the explosion that collapsed three floors of the administrative building in Petroleos Mexicanos' Mexico City headquarters complex, killing 37 people. He indicated the gas could have been either natural gas, which is used to fuel water boilers, or methane, a product of decomposition found in sewers and landfills.
