Gabriel Rentaria was 7 years old when he started using a gun. Never to kill, he said, just to scare people. But he saw people -- enemies and friends -- fall dead "in my face," he recalled.

Now 17 and a leader in a Catholic youth movement that reaches out to other young people trapped in a spiral of violence, Rentaria divides his short life into "before" and "after."

Left with an abusive father when his schoolteacher mother went to work in a distant city, he escaped to the street, spending as little time as possible with the man who beat him and shut him in "a hole," sometimes for several days at a time.

He was one of seven youngsters who hung out with a few 20-somethings, doing whatever they ordered -- stealing, selling drugs or shooting members of rival "combos," or criminal gangs.

It was a way to earn cash in a neighborhood where jobs are scarce and needs are great.

"To work, you need a diploma. If you don't have one, you can't get a job," said the soft-spoken, curly-haired teen, sitting on a wall beside St. Sebastian the Martyr Church near the edge of this tropical city.

This neighborhood, called Versalles 1, seems peaceful enough. Father Gustavo Piedrahita is celebrating Mass inside the church, while volunteers sell second-hand clothing, provide free haircuts and lead children's games on the fenced playground.

But there are telltale signs, if you know where to look. A few bricks are missing from the front wall of a house up the steep hill behind the parish. The two holes are just big enough to be used by a lookout or a gunman.

Rentaria and other young people from the Youth Leaders with Transformative Faith Movement are helping with a morning of activities designed to ease possible tensions between local residents and Venezuelan migrants who have arrived in the neighborhood.

It is one of many activities in which young people reach out to peers, offering them an alternative to the kind of life Rentaria knew as a child.

"The drug trafficking culture of Medellin has permeated much of society with very violent practices," said Carlos Henao, regional coordinator of the nonprofit Peacebuilding Institute Foundation, which has deep roots in Colombia's Catholic Church.

'Being a young person here means practically being destined to belong to some illegal armed group," Henao said.

Leaders of criminal bands in low-income neighborhoods prey on boys whose home life is unhappy, offering them affection in a "we've-got-your-back" style, explained Sebastian Restrepo, 22, who joined a combo when he was 4 or 5, determined to avenge the murder of his older brother.

Restrepo said he started using a gun at age 9 and drugs a year later. The leaders of criminal groups prefer to train children as killers, because if caught, they won't go to jail.

"I worry that kids see the leader of the group as a hero," said Father Piedrahita, 57, a Javeriano missionary who became pastor of St. Sebastian the Martyr nine months ago.

Drugs fuel much of the violence in the country, and children are caught up in it early, beginning with tasks such as selling drugs near schools.

"As long as drugs are the way to put food on the table, this is going to continue," Father Piedrahita said.

The risks for girls are equally chilling. Drug kingpins seek out teenage virgins for weekend parties outside of the city, paying the mothers as much as several thousand dollars. Both the girls and the mothers are trapped, because refusing would mark them for death, Henao says.

Amid the danger and violence, parishes offer refuge to children and teens, said Father Piedrahita, who sees his task as "building bridges between one situation and another, between one group and another."

Rentaria escaped from criminal life when his mother returned to Medellin and took him to live with her in a different part of the city.

"I told my mother everything. She cried and prayed for me," he said. "I put myself entirely in God's hands."

By age 10, Rentaria was a leader in a youth group. He finished high school and is now studying to repair airplane engines, but he also works actively to help kids who are trying to find a way out of the lifestyle that ensnared him as a child.

For Restrepo, giving up life as a criminal and a drug user was more complicated. Anyone who leaves a combo is marked for death, and he knows people who have been forced to take their families and flee the country.

Even while he was in the combo, Restrepo had begun attending youth activities in his parish. The members of the group accepted him despite his background and even when he was under the influence of drugs, he recalled.

It took a year of negotiating with the boss of his combo, who was especially fond of him, to let him go. Now 22, Restrepo said he has been drug-free for four years.

Milena Soto, 19, grew up in a stable, loving family that seemed far from experiences like those of Rentaria and Restrepo. But after high school, when she ventured out of her neighborhood to do social work in other parts of town, she began looking at the familiar streets with new eyes.

"Those kids standing on street corners, they weren't friends just hanging around. They were planning how to sell drugs somewhere, how to get a kid involved, that sort of thing," she said.

She saw gang members charging businesses protection money, saw children selling drugs at school doors as police looked the other way.

Asked what she would like Catholics in the United States to know about young people in Colombia, her eyes brim unexpectedly with tears.

"I'd like them to know the difference between life in their country and in mine," she said. "Sadly, ours is more violent, but that hasn't been our fault."

"If there were no consumers (of drugs like cocaine) there, there wouldn't be so much violence here," Soto said. "They are part of our history and we are part of theirs. There's a planetary interdependence."