Mexico's attorney-general says a deadly explosion at the headquarters of the state oil company Pemex was caused by a build-up of gas.
Jesus Murillo Karam says no traces of explosives were found at the site in Mexico City.
Several lower floors of the high-rise building collapsed in the explosion on 31 January, which killed 37 people and injured more than 100 others, the BBC reports.
Mr Murillo Karam says experts believe an electrical fault caused a spark that detonated the leaking gas, which may have been methane gas leaking from ducts beneath the building or from the sewer system.
