The Mexican military is trying to dismantle an extensive network of radio antennas built and operated by the notorious Zeta drug cartel. But the authorities haven't had much luck shutting Radio Zeta down. Not only is much of the equipment super-easy to replace. But the cartel has also apparently found some unwilling – and alarming – assistance by kidnapping and enslaving technicians to help build it.

At least 36 engineers and technicians have been kidnapped in the past four years, according to a report from Mexican news site Animal Politico, with an English translation published by organized-crime monitoring group InSight. Worse, none of the engineers have been held for ransom – they've just disappeared. Among them include at least one IBM employee and several communications technicians from a firm owned by Mexico's largest construction company. "The fact that skilled workers have been disappearing in these areas is no accident," Felipe Gonzalez, head of Mexico's Senate Security Committee, told the website.

"None of the systems engineers who disappeared have been found," Gonzalez said. Unlike Colombia, where drug traffickers control large amounts of territory and can keep hostages for many years, Mexico's drug territory is more in flux. "When they need specialists they catch them, use them, and discard them," said the father of one kidnapped engineer.

For at least six years, Mexico's cartels have relied in part on a sophisticated radio network to handle their communications. The Zetas hide radio antennas and signal relay stations deep inside remote and hard-to-reach terrain, connect them to solar panels, and then link the facilities to radio-receiving cellphones and Nextel devices. While the kingpins stay off the network – they use the internet to send messages – the radio network acts as a shadow communication system for the cartels' lower-level players and lookouts, and a tool to hijack military radios.

One network spread across northeastern Mexico and dismantled last year included 167 radio antennas alone. As recently as September, Mexican marines found a 295-foot-high transmission tower in Veracruz state. And while the founding leadership of the Zetas originated in the Mexican special forces – and who might have had the know-how to set up a radio system – relatively few of the ex-commando types are still active today.

One engineer, named Jose Antonio, was kidnapped in January 2009 while talking on the phone with his girlfriend outside a mechanics shop. He worked for ICA Fluor Daniel, a construction company jointly owned by U.S.-based Fluor Corporation and ICA, Mexico's largest construction firm. Antonio's family contacted the authorities, but were instead visited by a man claiming to be an ICA employee along with two Zetas. "They said they were going to help us, and that our contact would be ICA's security chief," said the kidnapped engineer's mother. But the group's message was implicit: Don't pursue this, or else. The cartel members were later arrested, but Antonio never returned.

Alejandro Moreno, an IBM engineer kidnapped in January 2011 while traveling from Monterrey to the Texas border city of Laredo, hasn't been heard from since. In 2009, nine contractors hired to build radio antennas in the border city of Nuevo Laredo – a Zetas stronghold – were kidnapped from a rented apartment by masked gunmen. They were taken with their vehicles and equipment.

Aside from the radios, the cartel's extensive weaponry alone caused *GlobalPost'*s Ioan Grillo to note "whether [the Zetas] should continue to be labeled as drug traffickers – or need a more martial description." Now add a military-grade communication system built with slave labor.

It'd also be one thing if jamming the radio network or tracking down and dismantling the equipment were enough to stop it. But that might not be enough.