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(CNN) Esperanza was waiting for her cousins outside her high school in Mexico one day, when a strange man drove up in a car, forced her inside with him and sped away. At that moment, Esperanza had in effect become a sex slave.

"He beat and raped me," she told CNN's "The Hunt with John Walsh."

She said the man -- who called himself Poncho — brought her to a madam who showed Esperanza how to charge clients and how to use a condom.

A few times Esperanza tried — and failed — to escape, but she said Poncho, now age 47, always tracked her down, and then beat her.

Eventually, Esperanza realized she was pregnant. Three months later, she said Poncho drove her across the Mexican-US border and on to Houston, Texas, where he forced her to work in a cantina called La Costenita.

She gave birth to a baby girl, but Poncho took the infant away as insurance that Esperanza would keep working as a sex slave and wouldn't escape.

Alfonso Diaz Juarez is accused of human trafficking in a Houston-area prostitution sting.

"I really wanted to speak up, to ask the police for help," Esperanza said. "But I got caught up by the threats he would make towards my daughter. I didn't want anything to happen to her."

Esperanza — whose real name is being withheld for her protection — had become just like the more than 19,000 sex trafficking cases reported in the US since 2007, according to the National Human Trafficking Resource Center

The site says more than 2,600 sex trafficking cases have been reported in the US this year alone, most of them in California. Texas ranks as the nation's number-two sex trafficking state, on the website.

A 'crime that happens in third world countries'

For the uninitiated, it's hard to imagine that thousands of young people — overwhelmingly women — have been kidnapped in Mexico or elsewhere and taken against their will to the United States, where they serve as sex slaves.

"I thought human trafficking was just this crime that happens in third world countries. Until I started to look into my city," said Rachel Alvarez, a human trafficking case worker for the Houston YMCA.

Texas authorities first met Esperanza when they raided La Costenita in 2010.

"Her initial demeanor was just kind of stoic," remembered Steve Roskey, who took part in the raid when he was an agent with the Texas Alcoholic Beverage Commission. "But then, all of a sudden, we noticed tears start running down her face. She started telling us her story: how she got here, what she was forced to do."

When she told police that her pimp, a man named Alfonso Diaz-Juarez who also went by "Poncho," was holding her daughter, authorities sprang into action.

"We knocked on Poncho's family members' houses, we knocked on his friends' houses," Roskey said. "It irritated the family and friends so much that (Diaz-Juarez) eventually dropped off the child to a cousin, and at about 3 o'clock in the morning, we got a phone call. The child was safe."

But Diaz-Juarez was nowhere to be found.

America's human trafficking 'hubs'

Pimps will often lure women from Mexico across the border to the US by promising them better lives, perhaps a better job, Alvarez said. These pimps may get help from people the women already know and trust, like a neighbor.

Once they're kidnapped, these women are no longer viewed as people in the eyes of their handlers. They've been reduced to a commodity that can be bought and sold repeatedly in an open market. In the United States, Houston has become one of those markets.

"People see Houston as a hub for human trafficking because of its proximity to the border," said FBI special agent Suzanne Bradley. "It also has access to the I-10 highway corridor, which goes across the country, so if they're smuggling people in and trying to get them into human trafficking in other areas of the country, it's very easy to get them on that I-10 route and disperse them throughout the country."

'One of the most violent pimps'

After the kidnapped women are brought into the US, the beatings begin as a way to keep them from trying to escape. Their captors threaten to hurt family members. Pimps use fear to keep their sex slaves in bondage.

"Poncho was one of the most violent pimps I've come across in the 11 years I've worked human trafficking," said Edwin Chapuseaux, a former investigator with the Harris County Sheriff's Office. "He did a lot of brutal things, bordering into torture, to make the girls do what he wanted."

A former sex slave we'll call "Laura" said Poncho knew her "mother's name, her address, everything. He would threaten me, tell me if I talked to anyone that he would hurt my family."

A pimp would have a lot to lose if a girl walked out the door.

"If a pimp has, let's say, four or five girls, and each one is making him, you know, $2,000, $3,000 a week, do the math, tax-free," said Chapuseaux. That works out to a maximum of $780,000 per year.

Laura recalls one night when she counted 70 women working. "The usual was 30 men. We each had to tend to 30 clients a night."

Teen girls available for $500 an hour

For years federal and local authorities had been gathering evidence against a huge Houston-area sex trafficking network led by Raquel Medeles Hortencia-Arguello.

The woman everyone knew as "Tencha" owned a brothel called Las Palmas that offered minor-aged girls to customers who would pay up to $500 an hour, according to the FBI.

Coincidentally, as a cautionary move, Tencha had distanced herself from Las Palmas by leasing it to Diaz-Juarez.

When police found out, they arrested him on a previous warrant.

Diaz-Juarez pleaded guilty in a deal with prosecutors that led to his release several months later. Poncho was back on the loose.

Following the money

Authorities continued to gather evidence in the big sex trafficking case.

"We realized early on that we had potential financial crimes, money laundering involved in the case, so we got the [Internal Revenue Service] involved in it," said Bradley. The IRS began following the money, reviewing bank statements, locating assets.

"We did an estimate on how much she made from the room rental, entrance fee, and the condoms for the whole entire period she was operating Las Palmas and that estimated to be about $12.5 million," said IRS Special Agent Lucy Tan.

When it was time for police to move in and raid Las Palmas, 13 people were arrested. Diaz-Juarez wasn't among them. But Tencha was.

Twelve pleaded guilty.

Prosecutors charged Tencha with one count of conspiracy to commit sex trafficking, one count of conspiracy to harbor aliens, three counts of money laundering and one count of conspiracy to money launder.

Tencha pleaded not guilty.

Anger triggers testimony

When Tencha began crying in front of the judge, saying she was innocent and she had no idea what was going on, it stirred something inside the freed women who once worked for her.

They began to get angry.

One by one they decided to take the stand and testify against their former captor.

"You didn't have to speak Spanish to see how much pain they had over what had been done to them, and what they had had to do," remembered Bradley. "You could just see it in their face, hear it in their voice."

Ultimately, the jury found Tencha guilty and the judge sentenced her to life in prison.

Despite the legal victory against Tencha, authorities are disturbed by the fact that Diaz-Juarez remains free.

"It's very important to get Poncho arrested and prosecuted, because he will not stop doing what he does until he is arrested and put behind bars," said Chapuseaux.

Laura, who still fears Poncho, admits she'll "feel safer when he is captured. There aren't any words to describe what a terrible person he is."