The Zetas are renowned as the most sophisticated and deadly of Mexico’s organized crime syndicates. Since setting up base in the coal-rich state of Coahuila, they’re quickly recognizing illegal coal mining as their best racket yet.

The Zetas have slowly taken control of Mexico’s third largest state, just across the Rio Grande from Texas, and begun overrunning local businesses – including the coal mines – through their usual strongarm tactics.

The gang reportedly mines its own coal through poorly paid workers, buys additional feedstocks from small, obliged miners, and sells the product to a complicit state-owned company.

Energy Tribune said the Zetas' annual coal mining profits in Coahuila were about $25 million a year, while Mexican daily Reforma estimated that criminals made $500,000 a week selling coal from unregulated mines to legal businesses.

As coal resold by the Zetas is thought to turn a profit 30 times greater than the initial investment, the group’s latest illicit enterprise is suspected to be its most fruitful.

“They discover a mine, extract the coal, sell it at $30, pay the miners a miserable salary... it’s more lucrative than selling drugs,” Coahuila ex-governor Humberto Moreira told Al Jazeera .

The violence and intimidation tactics familiar in headlines on Mexican drug trafficking are being used to silence coal operators from speaking out against the Zetas. Mine managers acknowledge a criminal infiltration, but offer few details on the killings, kidnappings and mutilations that keep the illegal fuel flowing.

Normal coal mining safety, meanwhile, has been all but completely ignored.

Even before the criminal influence, tunnel collapses and gas explosions were regular in Coahuila. A methane blast killed 65 people there in 2006.

Under the thumb of the Zetas, however, workers are being denied even basic safety protocols.

Mexican human rights officials say extreme poverty in the region means participating in illegal coal mining is not a matter of choice, and a lack of safety equipment represents little deterrent.

Coahuila generates 95% of Mexico’s $3.8 billion coal industry.