Officials contend that the blast was an accident...not sabotage...and that no explosives were found at the scene.
One woman is still reported missing.
Pemex officials now say a gas build-up...in the basement...probably methane...caused the explosion.
The exact source of the gas is still unknown...but their latest speculation is that gas leaking from water heaters...accumulated...for at least 7 months.
121 were injured from the blast in the heart of Mexico City.
52 remain hospitalized.
Most of the victims were women.
Firemen say a basement ceiling collapsed...trapping dozens of people.
A shift change was underway at 3:45 pm...when the explosion occurred in a building where 1,700 worked.
Media had speculated that a gas leak caused the blast.
Many survivors claimed they smelled gas before the explosion.
But an unidentified official said there had been a problem with electrical and AC equipment.
An AP reporter described the building as surprisingly decrepit for a major oil company...with slow, often broken, elevators...and dirty worn-out bathrooms.
But...narcos thugs have attacked some Pemex installations in the past.
Pemex reportedly increased security at all its facilities...while the blast investigation is conducted.
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