“Three months later, we still don’t have any ‘causa raiz’ (root cause) identified,” said George Baker, publisher of Mexico Energy Intelligence, a Houston-based report.

Gangsters also feed off Pemex. In one six-month period in 2012, crime syndicates stole more than 1.8 million barrels of oil from the company in more than 800 incidents, many of them involving illegal taps on pipelines.

President Enrique Pena Nieto, who came to office two months ago, has pledged to open the languishing energy sector to private investment, perhaps through a constitutional reform to ditch a ban on direct foreign participation. The powerful oil workers union, set up by the now-ruling Institutional Revolutionary Party, or PRI, is opposed to many facets of the reform.

Pena Nieto and a steady stream of cabinet-rank officials toured the blast site and the hospitals that were tending to the scores of injured. Also appearing amid the rubble were the chiefs of the army, navy and national intelligence agency.

“It’s a national security facility, one of the most important in the country even though it isn’t an industrial site,” said Christian Ehrlich, director of intelligence for Riskop, a Monterrey-based intelligence firm.

Ehrlich urged caution in analyzing the blast, but noted: “At the beginning of each administration, sometimes there are events that could be seen as a ‘show of force.’”

Small clandestine armed groups have attacked Pemex installations in the past. One of them, the People’s Revolutionary Army, or EPR for its Spanish initials, claimed to be behind a number of pipeline bombings half a decade ago. The group issued a statement late Thursday denying any link to the latest explosion.

Still, the more that Pena Nieto and other government officials urged the citizenry to desist from speculating about the cause of the blast, the more social media pulsated with talk that sabotage might have been involved.

“The tragedy of the Pemex tower has returned us to the culture of suspicion,” Francisco Garfias wrote in the Excelsior newspaper. “Pena Nieto felt obliged to ask not to speculate over what occurred. It did no good.”

Pemex has been at the center of several accidents with huge numbers of fatalities in the past three decades.

When a Pemex natural gas plant on the outskirts of Mexico City blew up in 1984, more than 500 people were killed in the catastrophic explosions.

On April 22, 1992, in Mexico’s No. 2 city, Guadalajara, gasoline leaked into sewers under the streets, triggering explosions over four hours that killed 252 people, tore up five miles of streets and left 15,000 people homeless.

While Pemex was implicated in the disaster, no full report was ever given.

“I don’t think the outcome was ever shown with any transparency,” Baker said.

Video: Search for Survivors in Mexico City Explosion