Their US training was designed to prepare them for counter-insurgency and, ironically, counter-narcotics operations, although Deare says they were not taught the most advanced commando techniques available at Ft. Bragg.
Military forces from around the world train at Ft. Bragg, so there is nothing unique about Mexican operatives learning counter-insurgency tactics at the facility. However, critics say the specific skills learned by the Zetas primed them for careers as contract killers and drug dealers.
“I think it is worth looking at [imparting some blame on the US for training founding members]”, Deare says.
About 29,000 people have died since Felipe Calderon, Mexico’s president, declared war on the drug cartels in 2006.
“The Zetas definitely have the reputation of being the most dangerous, the most vicious, the most renegade of the cartels,” says Kristen Bricker, a Mexico-based research associate with the North American Congress on Latin America (NACLA).
The group has mounted the severed heads of its victims on pikes in urban areas, posted torture and execution videos on the internet, forced poor migrants into prostitution and massacred college students during house parties.
"Other cartels have accused them of not following the 'gentlemen's code' of drug trafficking and causing undue violence," Bricker told Al Jazeera.
"At one time, it was considered bad form to kill pregnant women, but not any more." For safety concerns, Bricker didn’t want to say where she lives in Mexico.
Deare estimates "probably more than 500" GAFE personnel received special forces training on a yearly basis. He is unsure exactly how long the programme lasted. The Zetas came to the attention of Mexico’s Attorney General’s office in 1999.
After US training, GAFE operatives defected from the Mexican military to become hired guns, providing security to the Gulf cartel, a well established trafficking organisation, according to Laura Carlsen, director of the Americas program of the International Relations Center.
"They split from the Gulf cartel and formed as a cartel in their own right," Carlsen, based in Mexico City, told Al Jazeera.
The Zetas' alleged current leaders, Heriberto Lazcano, known as Z-3 and Miguel Trevino, or Z-40, were first recruited by Osiel Cardenas, the now-jailed leader of the Gulf cartel. The name "Zetas" originates from the radio code "Z" used by top military commanders in Mexico.