The Phoenix Police Department receives nearly 10,000 missing person reports every year. In May 2001, one of the reports was for 17-year-old Alissa Turney.
On the last day of her junior year at Paradise Valley High School in Phoenix, Alissa was reported missing by her stepfather, Mike Turney, who told police he had picked Alissa up early from school, taken her to lunch and then dropped her off at home.
"She seemed like she was happy," Turney said of the father-daughter lunch. "She was thinking about the summertime."
But over lunch, a fight developed between Turney and his stepdaughter about his rules and her behavior.
"She wanted to ... be able to stay out later at night, and not be accountable to where she was at. And I told her, 'As long as you're under my roof, we're gonna have to, uh ... check in with Daddy, 'cause Daddy's a nervous wreck if you don't," he said.
When the two returned home, Alissa stormed off to her bedroom -- visibly upset, according to her stepfather. Leaving Alissa at home, Turney went to pick up his other daughter at school and said when he called Alissa a few hours later, there was no response.
"My dad picked me up and said, 'Your sister's not answering her cell phone. Will you try to call her?' And so we were just in the car calling, calling, calling. Got home, she wasn't there. You know, my dad was running through the house," Sarah Turney, Alissa's younger sister, told ABC News.
With Alissa nowhere to be found, Turney said he found a note in her bedroom, which said she was running away to California. Sarah Turney said her dad immediately began to panic.
"I'm the younger sister. I'm like 'She's just doing whatever, she'll be right back.' But my dad went right to work," Sarah said.
Turney said he canvassed the neighborhood, visiting Alissa's favorite hang-out spots and calling her friends. None of Alissa's friends had seen or heard from her. So, Turney contacted police and filed a missing person report. But given Alissa's age and the note she left behind, Alissa was considered a runaway.
CLICK HERE to see photos of Alissa through the years.
If you have information that might help solve the mystery of what happened to Alissa Turney, please contact the Phoenix Police Department on their website, http://phoenix.gov/police/, or by phone 1-480-WITNESS, 1-480-948-6377.
"I think for the first couple weeks I just thought she was hiding out a friend's house," Sarah Turney said. "I mean she, you know, she was seventeen, so she was always like, I don't want to live here. I shouldn't have to live by these rules. I never thought she would do it."
For most of the people who knew her well, Alissa's runaway note didn't come as a complete surprise. Even as a little girl, Alissa had a bit of a rebellious streak.
"She was quite a handful. A little pistol," said her stepfather. "Some might call it difficult to deal with but ... I took it as a challenge."
When Alissa was 3 years old, her mother, Barbara Strahm, met and married Turney, an electrician and former sheriff's deputy who had three boys from his first marriage. Along with Alissa, Strahm had son John, 10, from a different biological father. Rounding out their "Brady Bunch" combined family, Barbara and Turney had daughter Sarah, and Turney officially adopted Barbara's children.
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.
"Alissa had told [her friends] very graphic things, very disturbing things," said Andersen. "You have a potentially dangerous family secret there and a child who's never been seen again, you put those together, you have to start looking for who would benefit from her disappearance."
Click here to read ABC News' full interview with Michael Turney.