Zetas' alleged current leaders, Heriberto Lazcano, known as Z-3 and Miguel Trevino, or Z-40, were first recruited by Osiel Cardenas

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. 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.

But unlike Zorro, the Mexican outlaw hero who also used the "Z" alias, Los Zetas steal from everyone, not just the rich. And they certainly don’t give much back to the poor, except the corpses of their relatives. "They are just known for being a different kind of human being," says Bricker.

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