But in 1993, tragedy struck when Barbara was diagnosed with cancer. She died just a year later, when Alissa was only 8 years old. Turney was left to raise two young girls alone, and as Alissa entered her teens, they experienced friction.
"She was just very naive to many things," he said. "Didn't comprehend the repercussions of what she did."
But Alissa's best friend, Katie Rothweiler, described her as a normal teen, who was simply more interested in her friends and her boyfriend than schoolwork. Katie remembered Alissa often clashing with her father's tough love style of parenting.
"It was very hard for her," Rothweiler said. "She would always have to worry about him going through her things all the time. He was very, very strict."
Many of Alissa's friends thought she had finally had enough of her life at home and decided to start anew. But after several months, people close to her began to wonder why they had never heard from her.
"There is no way, no way, I know for a fact, that she would not have contacted any of her friends," said Rothweiler.
Another friend, Charity Thompson, said Alissa depended on her friends. "Years start passing, and I think that's the point where those heavy feelings really start to settle in, and you really start to wonder."
Alissa's stepfather said he also began to fear the worst. He had spent three years in law enforcement in the 1970s, and tried everything he could think of to find Alissa, including posting fliers about her, talking to her friends and taking trips to California to find her.
Then in 2006, five years after Alissa disappeared, Turney received a call from a Phoenix police detective, who told him a convicted killer in Florida had confessed to murdering Alissa.
"It's devastating," Mike said. "[Because] I've still got in the back of my mind ...t here's a possibility this kid could show back up, because there's so many things I want to say."
After he was sentenced to life in prison in 2003, Hymer began writing letters to local investigators. In his letters, he described killing 21 women -- mostly adolescent girls who, like Alissa, seemed to have simply vanished.
Special agents from the FBI stepped in and interviewed Hymer in prison. During one of those visits, Hymer successfully identified Alissa from a photo line-up. The information was then handed over to the Phoenix Police Department, and Will Andersen and Stuart Somershoe, two detectives from the missing persons unit, were assigned to the case. With little progress made on Alissa's case during the seven years since her disappearance, they were essentially starting from scratch.
"We had to get to know Alissa," Andersen told ABC. "We had to get to know what kind of person she was to be able to look at Hymer, to address Hymer, and determine whether he had met this girl."
But from the beginning, something about Alissa's case just doesn't seem right.
"We learned that she had a large amount of money in her bank account. When a runaway leaves, they take things with them. They take their money, they take their personal possessions," said Somershoe. "Alissa didn't take anything with her."
And as the two detectives looked closer, then began to hear some troubling stories about Alissa's life at home.