It ended 20 years later, when Gonzalez is accused of killing Ana and leaving her body under a blanket behind a sofa.
In between, officials say, Gonzalez fathered children with both Ana and her mother, throwing a poor immigrant family from El Salvador into chaos.
Ana's older brother Hugo remembers the night he learned of his sister's abuse. Gonzalez had been living with their mother, Lidia, in their Torrance, California, home. Over time, he had become a surrogate father figure to Lidia's children.
"My mom was sick in the hospital. We all slept in one room. I couldn't sleep that night, so I was actually awake. I witnessed Tomas walk in, [wake] my sister up, and told her to follow him. They did not know I was watching."
Hugo recalls seeing Gonzalez forcing himself on Ana. "I got scared, walked back into the room, and waited for my sister to return."
When she came back to their bedroom, Hugo confronted her. Ana told him, "Well, it's something I have to do, because if I don't do what he says, then he's going to leave my mom ... I want you to promise me that you will never say anything."
It's a threat that is common among pedophiles, according to John Walsh, host of "The Hunt." "Usually they're children of divorce to begin with, so this huge burden of guilt is that we're going to be abandoned, we'll be poor again or we'll be less fortunate again. But most of all: it'll break mommy's heart. It's disgusting."
Hugo reluctantly agreed to keep their secret, a decision that still haunts him. "What would have happened if we wouldn't have waited so long? Maybe I would still have my sister?"
Fathering children with mother and daughter
Around the same time that Gonzalez began to secretly abuse Ana, he fathered a child with Ana's mother. According to police, Gonzalez continued to molest Ana throughout her childhood and teenage years.
Things changed -- though not for the better -- in 1994. Lidia, growing ever suspicious, came home early from work and caught Gonzalez and Ana, now 15, in the act. After a confrontation, Lidia threw Gonzalez out of the home. Soon after, Ana left to live with her abuser.
"She has no friends, and she has this man who has his own place, and has his own job," according to Los Angeles County Sheriff's Detective Richard Ramirez. "That's why she went ahead and ultimately ended up living with him."
While living together, Ana and Gonzalez had a son, Moises. Ana would keep secret the identity of her son's father for the rest of her days.
Soon after, Ana reconciled with her mother and moved home with Moises. Eventually Gonzalez also reconciled with Ana's mother and moved back into the home.
"Tomas came to the house to speak to my mom," Hugo told "The Hunt." "I guess he went with the intentions of convincing her for him to move back. So, she ended up accepting him."
Gonzalez resumed his relationship with Lidia and, about a year later, they had their second child, Gabriela.
"Now he has a kid with my mom, and the kid with my sister at the same time. And they're only about a year difference. And now we're all living together."
Lidia and Ana's youngest children were brought up thinking they were cousins when, in fact, they were half-siblings.
This strange arrangement continued until 2001 when Lidia died of lung cancer, leaving Tomas, the lifelong abuser of her daughter, in charge of the family. Tomas and Ana continued their relationship, producing one other child together, Raquel.
'What did he do to her?'
In 2007, at age 28, Ana began dating for the first time. Gonzalez was enraged, unwilling to let Ana out of his control. According to Hugo, he threatened her with a gun and told her "[if] you ever leave me for any other guy, I will kill you."
Gonzalez had taken advantage of her since she was 9, according to Ramirez, who said he believes "he wasn't going to allow her to be with anybody else, to have any happiness in her life."
On September 12, 2008, Hugo was at home with the children when he got a call from Ana's work. She hadn't shown up and wasn't returning messages. Her purse and shoes were still at home.
Hugo was beginning to worry when he got a call from Gonzalez's brother, who told him, "Once you clear the kids from the apartment, call me."
"I spoke to him, like, man to man," Hugo told "The Hunt." "What he do? What he do to her?"
According to Hugo, Gonzalez's brother revealed that Gonzalez had confessed to the killing, and that Hugo would find Ana "under some blankets" in the family's living room.
Gonzalez fled to Guadalajara, Mexico, according to police, along with money from Lidia's Social Security benefits that was intended for her children.
With his mother and sister dead and his stepfather a fugitive wanted for murder, Hugo committed himself to holding what was left of his family together. Now he takes care of both Lidia's and Ana's children, as well as his own
"We don't like calling each other brothers and sisters," Hugo told "The Hunt." "We just go based on nephews and uncles. We're trying to put everything behind us."
All that remains is to bring Gonzalez to justice.
"It's not over until he's caught," Hugo said. "None of this is over until he's actually caught."
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