An explosion at the headquarters of Mexican state-owned oil firm Pemex was caused by a gas build up, the attorney general has said. The blast on Thursday killed 37 people and injured dozens more.
A four-day investigation into last week's blast determined Monday that a rumored bomb attack was not to blame. Mexico's Attorney General Jesus Murillo Karam said a team of investigators found no trace of explosives at the site.
"We have been able to determine that the explosion was caused by an accumulation of gas in the basements of the building," the attroney general told a news conference.
He said the gas, believed to have been methane, came into contact with a spark, triggering the blast.
"This caused a defect in the structure of the floors, which first were pushed upward, and then fell, which was the main cause of death in the building," Murillo said.
Some 37 people died in the blast at the complex that houses the offices of Pemex in Mexico City on Thursday. At least 120 people were injured.
It was the latest in a series of safety lapses which have plagued the company in recent years. Last year, 30 people were killed by an explosion at a gas plant in Reynosa, near Mexico's border with the United States.
ccp/msh (AFP, AP)