California Teen 'Romeo and Juliet' Suicide Pact Goes Awry After Mom's Murder

Sept. 16, 2011 — -- Tylar Witt still brags about her mom.

Joanne Witt's master's degree in mechanical engineering, her skill in the kitchen and her tomboy traits are all sources of pride for her teenage daughter.

"She was a lot like a dad," Tylar said. "What other mom catches snakes and lizards and puts them in aquariums?"

But the affection Tylar shows today was critically absent on June 12, 2009 -- the day, prosecutors say, Tylar helped her boyfriend kill her mother.

Watch the full "20/20" episode, "Star-Crossed Teen Killers," online here.

"I don't think I ever appreciated what my mom did for me," she told "20/20." "When you are a kid, the only thing that you see are [parents] doing stuff for you and then them punishing you."

Joanne Witt was a single mother raising her only daughter in a wealthy gated community in El Dorado Hills, Calif. She stopped seeing Tylar's father while she was still pregnant and was determined to raise Tylar on her own. An accomplished engineer, Joanne Witt provided her daughter with everything from acting courses and riding lessons to adventurous site-seeing trips. They also spent quiet evenings at home, cooking together and watching movies.

But moments of mother-daughter bonding were belied by a long-standing friction.

When Tylar was in pre-school and a teacher noticed suspicious bruises on her face and body.

Tylar's aunt, Mary Witt, said that Joanne Witt once flew into a rage while driving Tylar, who was then a pre-schooler. She pulled the girl out of the car, hit her with a belt and slapped her.

"She was just bruised all over," Mary Witt said.

Tylar's pre-school teacher noticed the bruises and informed authorities. Tylar was taken away from her mother for several months and Joanne Witt was ordered to take anger management classes. The mother vowed never to let something like that happen again.

Tylar said there were no more beatings, but there were loud arguments, often fueled by what Tylar says was her mother's secret drinking problem. Another source of tension was Tylar's questions about her biological father -- questions Joanne Witt didn't want to answer.

Joanne Witt "didn't want him in her life," Mary Witt said.

But the biggest battle would come when Tylar turned 14. She met an older boy, 19-year-old Steven Colver, at a shopping center. Nicknamed Boston, Colver dressed in black, Goth clothing but had a job, attended community college and, according to Tylar, was a great listener.

PHOTOS: Tylar Witt and Steven Colver

"I had a really, really bad day," Tylar remembered. "I called him up and said 'I just need someone to talk to.' He would come by my house and we would just talk."

Tylar started calling him her "big brother" and they told Joanne Witt they were just friends, as close as a brother and sister. Tylar even told Joanne that he was gay, according to Mary Witt.

Joanne Witt was so comfortable with Tylar and Colver's friendship that when Colver needed a place to live, she invited him to live in a spare room in the house for $500 a month.

"He was going to be part of the family," Mary Witt said.

But soon there would come clues that Tylar and Colver were more than just friends. Mary Witt said Joanne noticed the two were "a little more chummy" than she had anticipated.

A surprise visit to Colver's room soon confirmed her suspicions: She found both of them there and Tylar was naked, hiding in the closet.

"She found out that they were having sex there and she just couldn't believe it. She just started screaming, you get out of here," Mary Witt said.