Taken: The Amber Dubois story

Convicted killer John Gardner reveals harrowing moments leading up to the murder of Calif. girl; Says he'd kill again

Supervising Producer, Katherine Davis; Producer, Grace Kahng

For a year and a half, from the time 14-year-old Amber Dubois first went missing, "48 Hours" was with her anguished extended family. You'll learn how the strain of her disappearance wore them down and, for a time, tore them apart.

It has been 22 days since Amber Dubois disappeared, and the desperate search for the straight-A student is in high gear.

More than 400 volunteers are combing 200 square miles of countryside on foot.

The crisis has brought together a fractured family: Amber's mom, Carrie McGonigle; Amber's father, Moe Dubois; and Dave Cave, the man Carrie now lives with.

"Every morning she'd wake me up before she left for school and give me a kiss …and tell me she loved me," Carrie tells "48 Hours Mystery" correspondent Troy Roberts.

"Amber lives at my house. And I come home to her every day. She's my daughter to me. She's my baby girl," says Dave Cave.

It's the spirit of a special child that keeps their hopes alive.

"My daughter Amber is my sweetheart," Moe Dubois says. "She's a little girl who always has a little smirk on her face, teases me all the time … gives me a hard time about my receding hairline. That's my kid."

"She loves to read," adds Carrie. "She has friends at school and stuff, but she doesn't go to the mall. She hates to shop. She doesn't wear makeup… she's a bookworm."

But as the days pass with no breaks in the case, the stress starts taking a toll on all three parents.

"This is tearing Carrie's heart out of her," Dave Cave explains. "She's just - I hate seeing what it's doing to her."

"It consumes you, you know," Carrie says. "You don't know where your daughter is, your child is. It just changes your whole, your whole world

"I don't want to make it to a month," Moe says. "I want a hug tomorrow. I want a hug tonight. I want to see someone call us tonight and say, 'We've got her, she's coming home.'"

The mystery of Amber Dubois' disappearance began on the day before Valentines Day, Feb. 13, 2009.

"Amber, she'd been waiting for a year for this day. She's been into animals since she was still in diapers," Carrie says. "Her science project is to raise a baby lamb. She was all excited when I left that morning, she's like, 'Thanks Mom, I love you so much, thank you for the lamb.'"

Amber was last seen around 7 a.m. just blocks from Escondido High School.

"She was seen by two different parents walking up the street," Carrie tells Roberts. "She was walking by herself the first time… and the second time, there was a man standing next to her or a kid."

When Amber didn't show up at home by 4:30 that afternoon, her stepfather, Dave, went looking for her.

"I went to her first class and her teacher told me that she had not shown up to class and immediately I knew something was wrong," he says.

"I get a call from Carrie saying "I don't know where Amber is. [She's] hysterical. In tears," Moe recalls.

Her panicked family went into immediate search mode, retracing Amber's route to school, plastering the town with flyers and knocking on every door in the neighborhood.

Nobody in Amber's family is willing to give up hope - even the smallest member, Dave and Carrie's 7-year-old daughter, Allison.

"She'll hear people say kidnapped or abducted and she'll kind of freak out, you know. 'Amber's not kidnapped' and she wants to search, so we go on walks with the dogs and we go search for her sister because she wants to. She wants to participate," says Carrie.

Amber's father, Moe, puts his life on hold, taking a leave from his job as an electrical engineer in Los Angeles and moving to a nearby hotel with his partner, Rebecca Smith.

"Usually end my night by about two or three hours of crying," he says. "I have to have my point to release… If volunteers and everyone around here starts to see my frustration… then it'll trickle on through them."

As the days pass, hope begins to fade, replaced by a growing suspicion that Amber may have met with foul play in her own home.

Escondido police begin focusing on one member of the family in particular: Amber's stepfather, Dave Cave.

"How soon after her disappearance did you realize you were a person of interest?" Roberts asks Dave.

"I don't think it actually really set it for me for a couple of weeks," he replies. "The head searcher said, ' You can't be involved in the search because you do not want to be the person who finds Amber.' And I looked at them like, 'Why not?' And they said, 'If you're the person who finds something, they're going to pin it on you.'"

Dave, who was the last person to see Amber, walked "48 Hours" through what he says happened the morning she disappeared:

"Amber was up and ready to go to school on time without any prompting, because she knew she was getting her check to get her lamb," he says.

"About when I was finished getting dressed, Amber came into my room and said, 'Dave, have you got my check for the lamb?' And I said, 'I'll give it to you before I leave sweetie.' So she came up several times and I think it was the fourth time that she asked for the check. I said, 'Sweetie, I will give you the check before I leave, just go downstairs. You'll have the check. I promise. Just relax.'

"So I came downstairs and I sat down at the table… and I wrote out the check for the lamb… I sat the check down on the arm of the couch and Amber was sitting on the floor… she was eating a bowl of cereal. And I said, 'Sweetie, here's your check for your lamb. I'll see you later I love you.' And I turned around and walked out of the door and went about my day."

That was the last Dave saw of Amber.

But it was what this man of routine did not do that quickly made him a key suspect. Dave Cave did not show up for work that day. He says he went to the gym and then home to do his taxes.

"When I came back to the house, she was gone. So I figured she went to school, she should have been at school by then," he tells Roberts.

While he was at home, Dave somehow did not get the message from the high school secretary alerting them that Amber - the girl with perfect attendance - had failed to show up at school.

"Fairly early on into the investigation, suspicion was swirling around your partner Dave," Roberts remarks to Carrie. "But eventually, you became suspicious as well."

"You know, Dave had come to my work that day and brought me some chocolate covered strawberries and some roses that day," she says. "It was for Valentine's Day - it was the 13th. Except that Dave doesn't celebrate Valentine's Day… And he stuck around for like 45 minutes that day. And I'm like, I had to ask him to leave. I'm like, 'Dave, what are you doing here. Go.'"

Another concern for investigators centers on some tension between Dave and Amber that led the family to counseling.

"Amber and I didn't always get along perfectly," Dave admits. "In a house there's rules. She's a teenager. She doesn't want to follow the rules. There's going to be a certain amount of conflict."

"They really didn't talk for the whole month before Amber went missing," Carrie says. "It was a constant bicker."

Dave claims the night before Amber disappeared, they finally called a truce.

"I know the night before she went missing we went out and went shopping and went to the bookstore and stuff and we had a really good time," he recalls.

Could Amber possibly have said or done something the next morning to set Dave off?

Escondido police are taking a hard look at Dave and the answers he gives police will raise Carrie's suspicions even further.