What Made Houston Teen Kill Her Friends?

Sept. 25, 2009 — -- In the spring of 2003, things were looking up for 17-year-old Christine Paolilla, a shy teenager who had always struggled to fit in. She was friends with two popular girls at school -- Rachael Koloroutis and Tiffany Rowell -- and she had been voted "Miss Irresistible" by the student body at Clear Lake High School in suburban Houston.

But on the afternoon of July 18, 2003, Paolilla's life changed forever. Four youths were found shot multiple times at point blank range in a home in the placid Clear Lake neighborhood. Two of the victims were her friends, Koloroutis and Rowell, who had recently graduated. Koloroutis was planning to attend college in the fall.

The police were stunned, and stumped as to who would want the youths dead. "There was a lot of rage and anger behind these killings and so, therefore, we thought ... perhaps there was a personal relationship between the victims in the home and the killer," Houston Police Sgt. Brian Harris told ABC News.

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It would take three years to unravel the mystery. After numerous dead ends, police caught a big break in July 2006, when an anonymous tipster called. The tipster described facts only the killers could have known and gave them two names -- a boy, Chris, and a girl: Christine Paolilla.

Christine was arrested, tried and convicted of the crime. "Chris" was Chris Snider, Christine's boyfriend in high school, who committed suicide after he learned police were on his trail.

The question that haunted everyone, including the police, was, "Why?" The details didn't seem to add up. Rachael and Tiffany had befriended Christine and offered her advice, including beauty tips. The friends even carried pictures of each other in their wallets.

Why would Christine want to kill her friends?

Christine's parents, Lori Paolilla and stepfather Tom Dick, spoke to "20/20" exclusively about their daughter's life before July 18, 2003.