By CNN Staff — A buildup of gas was responsible for last week's blast that killed at least 37 people at the offices of Mexico's state-run oil giant, the country's attorney general said Monday.
Mexican Attorney General Jesus Murillo Karam told reporters no traces of explosives were found.
The blast took place Thursday at an administrative building in the Pemex office complex in Mexico City.
Pemex is Mexico's powerful and much-criticized state oil monopoly.
Thousands of people work at the Pemex headquarters, which includes a 54-story building that is nearly 700 feet tall. The annex where the explosion happened is adjacent to the tower.
-- CNNMexico.com contributed to this report.
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