(NewsNation) — The last time Ava Grace Baldwin’s father saw her, she was 6 years old. Eight years later, he believes his ex-wife took Ava and has been hiding her for years and thinks his daughter may not even know she’s a missing person.

Ava was reported missing from her elementary school, having not shown up for nearly three weeks when the school contacted her father. Police think her mother took her and Ava’s father has been on an eight-year quest to find her.

David Hopper got the call from his daughter’s elementary school in September 2015. Ava hadn’t been in class for 21 days and the school wanted to know if he knew where she was.

Ava and her mother, Kathryn Baldwin, lived in San Antonio, Texas while Hopper lived in central Oklahoma, a seven-hour drive away. Ava was born to the couple after a 34-day marriage.

When the school contacted him, Hopper called the San Antonio police to report 6-year-old Ava missing. What police found surprised them.

“When we sent the police out to the location of the last address we had, it turned out to be an empty lot. And that’s when we figured there’s something going on here,” Hopper said.

Hopper said from the moment Kathryn told him she was pregnant, he tried to be the father Ava would want and need.

But it was difficult for him to have the chance. Hopper hired five different lawyers and spent more than $45,000 battling for a custody arrangement in courts in Texas and Oklahoma

“She’s just the perfect little girl,” Hopper said. “She was surprised to know she had so much family on this side.”

While Hopper fought for custody, he said Kathryn’s life was spiraling. She was in and out of church missions, shelters and relationships, he said, as he fought for more access to Ava.

Hopper said one day, Child Protective Services was alerted to a video of Kathryn performing a solo sexual act while 2-year-old Ava was in the bed behind her.

“CPS contacted us and said, if you can help us find her, we have your daughter,” said Tina Fullbright, Ava’s aunt.

But after that, Hopper was only given partial custody. He drove seven hours each way to pick up Ava for a month in the summer and holidays. He recalled what Ava said to him one of the first times he took her swimming.

“You’re my Daddy, you’re my Daddy,” he recalled. “She did not know she had a father. She was in awe she even had a father. I was kept a secret from her, I guess.”

Fullbright said Kathryn, also known as Katie, had a habit of running.

“She’d just jump counties. She’d get in trouble in one county and just move to another county,” Fullbright said.

Kathryn has a felony warrant for interfering with child custody. Police records show she had a history of alcohol and prescription drug abuse and suffers from mental illness.

But when Hopper requested full custody due to his concern about Kathryn’s ability to keep Ava safe, Kathryn and Ava disappeared. Kathryn’s vehicle, a silver 2014 Ford Escape, was found abandoned in a San Antonio park in April 2016, seven months after the pair vanished.

Ava would be 14 now and Hopper has been awarded full custody. But he has a theory that Kathryn’s family may be hiding the pair. However, there is no proof and police have had no new leads when it comes to locating Ava or her mother.

NewsNation spoke with Kathryn’s other daughter, now an adult, who was raised by an adoptive family. She was afraid to appear on camera but told NewsNation she fears Kathryn and Ava were taken. She said her mother had a very traumatic life and often trusted the wrong men.

Still, police are investigating the case as a non-custodial parent abduction.

Hopper remains hopeful that Ava is alive. He said there have been sightings of the pair since they disappeared, including contact from a couple in Florida who said Kathryn tried to hand over custody of Ava to them.

“There’s reason to believe Ava’s alive. There’s a case down in Florida where we know the couple that she tried to give Ava to, they contacted us, and that was in 2016,” Hopper said.

San Antonio police said there was another possible sighting of Kathryn as late as 2020. They confirmed they have records of her using nearly a dozen aliases.

Hopes rose again in 2022, when armchair detectives thought they spotted Ava and Kathryn in a series of TikTok videos featuring a mother-daughter duo by the names of Bebop and Bebe. Rolling Stone magazine even featured the story.

“We had that investigated, it turns out it wasn’t them,” Hopper said. “But the only great thing about that is it brought a lot of attention to her case. In fact, it went viral overnight, so we can’t complain about that.”

For now, Hopper and his family post letters to Ava on a Facebook page, hoping that one day she’ll stumble across it and see how much she is loved and missed.

“It’s hard to watch my brother go through this. This is his only child,” Fullbright said. “That’s all he’s ever wanted, a family, and he deserves to have his daughter in his life.”

Hopper said sometimes he has to distance himself from his daughter’s disappearance because not knowing where she is eats him up inside.

“You ask me if she’s still alive.  Sometimes, I have my doubts, I’ll be honest with you, but when you ask me I answer with confidence because I believe that God is true to his word,” Hopper said. “That he said he would watch over her, that he would protect her that he would keep her safe.  And that he would bring her home one day.”