CIUDAD JUAREZ, Mexico — At less than 5 feet 6 inches with acne and a mop of curly hair, 17-year-old Jose Antonio doesn’t look particularly menacing.

But in his tender years, he has seen more firefights and murders than many soldiers serving in Iraq or Afghanistan.

Indeed, Jose Antonio has come of age in a war zone. And he has served as a soldier, siding squarely with the insurgent drug gangs of Juarez.

He said he first picked up a gun at 12 years old, when he joined the calaberas, or “skulls,” one of the gangs that rule the slums that climb up sun-baked hills on the west side of this sprawling border city.

By 14, he had his hand in armed robberies and drug dealing and was involved in regular gun battles with rival gangs, he confessed to police.

At 16, he was nabbed for possession of a small arsenal of weapons — including two automatic rifles and an Uzi — and accessory to a drug-related murder. He was sentenced to three years and one month in the “Juarez School of Improvement,” the city's juvenile detention center known more for the hardened and desperate young adults who emerge than for any kind of improvement.

“Being in shoot-outs is just pure adrenalin,” he said, smiling, as he sat in the youth prison’s dining area behind a towering outer wall that is protected against gunfire by sandbags and guards hidden behind ski masks for their own protection.

Teenagers and young men like Jose Antonio provide a vast army of recruits for the drug cartel armies, which produce cheap assassins-for-hire who have drowned the streets in blood.

There have been more than 5,500 murders in Juarez since January 2008. More than 1,400 of the victims, or about a quarter of the total, are under 24.

Watch a video about inmates who believe turning to Jesus can help stem the violence:

Back in the 20th century, Mexican "gatilleros," or triggermen, were mostly older professionals, who dispatched their victims in the dark of the night — a life described in a 1983 book “The Black of the Black,” by Jose Gonzalez.

“I started killing at age 28 and in my conscience know of more than 50 individuals I have sent to the other world,” wrote Gonzalez.

But in the explosive war for control of Juarez’s trafficking routes and street corners, many killers are teenagers or in their early 20s, enlisted from bloodthirsty street gangs.

While the older triggermen used to make small fortunes for their sanguine trade, gang members say they will now carry out a murder for as little as $100.

“There is killing every single day. So now it’s no big deal,” Jose Antonio said, unblinking. “You see dead bodies and you feel nothing.”

Prison authorities agreed to let Jose Antonio and other inmates speak on the condition that full names or photos not be used. Speaking to the press can be seen as informing and alleged "suplones," or snitches, are regularly murdered here.

The School of Improvement now holds 63 inmates under the age of 19, convicted of crimes including homicide, kidnapping and rape. More than 90 percent are gang members, said prison psychologist Elizabeth Villegas, but they represent only a tiny fraction of the tens of thousands of gangbangers on Juarez’s streets.

“Most come from broken families and don’t recognize rules or limits,” Villegas said. “They don’t feel anything that they have murdered people. They just don’t understand the pain that they have caused others.”

Drug cartels know that teenage assassins face little time in jail. Under Mexican law, a minor can receive a maximum sentence of five years whatever the crime. If the same deeds were committed over the border in Texas, they could be imprisoned for up to 40 years, or for life if they were tried as adults.

Jose Antonio’s family is typical of those populating the slums that have sprawled on the outskirts of Juarez in recent decades.

His parents immigrated from a country village in the southern state of Veracruz to sweat for $6 a day in assembly plants owned by Japanese and American firms.

While they held old-fashioned country customs, celebrating village saint days and respecting the power of local patriarchs, he grew up in a city of 1.3 million, flooded with drugs heading north, and guns and contraband consumer goods flowing south.

His parents labored for long hours on production lines, leaving him alone for much of the day and he quickly become involved in the “Calaberas” street gang.

"The gang becomes like your home, your family. You feel part of something,” he said. “And you know the gang will back you up if you are in trouble.”

A recent study found that 120,000 Juarez youngsters aged 13 to 24 — or 45 percent of the total — are not enrolled in any education or do not have any formal employment.

Drug cartels step in to provide jobs, using their operatives in the slums to look out for talented young gunslingers for hire, the imprisoned gang members explained.

The incorporation of street gang members into the cartel armies has lead to bloody repercussions.

When a few members of a gang are identified as working for a cartel, a rival cartel often tries to wipe out the entire gang, massacring the youth of certain neighborhoods.

The mother of one imprisoned gang member showed a deserted street corner outside her home.

“A year ago there was about 20 kids hanging around here. Now almost all of them have been killed,” she said, asking her name be withheld in case of repercussions. “I am glad my son is in prison or else he probably would have been murdered by now too.”

Social worker Sandra Ramirez counsels teenagers in the slums and has seen dozens of youngsters get recruited into the ranks of organized crime in jobs including look-outs and drug sellers as well as assassins.

She said that parents here often neglect their children, with many broken homes and demanding jobs in assembly plants or in the city’s huge sex industry.

“We have been a permissive society and let a lot of things pass,” she said. “I work with one 14-year-old, whose parents are broken up and each has a new family. He doesn’t feel he has a family himself so he spends all day on the street and that is where he has started criminal activities.”

However, she said the government has also grossly disregarded the slums, failing to provide adequate schools or job opportunities.

“The government just puts Band-Aids on the problems ... . It is only them (the cartels) that are coming to these kids and offering them anything,” Ramirez said. “They offer them money, cell phones and guns to protect themselves. You think these kids are going to refuse? They have nothing to lose. They only see the day to day. They know they could die and they say so. But they don’t care. Because they have lived this way all their lives.”

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Timeline: the meltdown of Juarez