A HIGH SCHOOL CINDERELLA STORY THAT ENDED IN MURDER, AIRING ON "20/20," FRIDAY, JANUARY 7 AT 10:00 PM ET

Why did high school outcast Christine Paolilla, who was transformed from an ugly duckling into "Miss Irresistible," turn on the very girls who made her popular? On a hot, quiet July 2003 afternoon, four recent high school graduates, including Paolilla's two best friends and the most popular girls in school, Rachael Koloroutis and Tiffany Rowell, were gunned down at Tiffany's home in a Houston, Texas suburb. Police were baffled by the murders, which were seemingly random. But as police dug deeper in an investigation that dragged on for three years, they discovered that the killer might be closer to home than anyone ever expected. Was Christine Paolilla responsible for murdering Rachael, Tiffany and two others? ABC News Correspondent Deborah Roberts' report airs on "20/20," FRIDAY, JANUARY 7 (10:00-11:00 p.m., ET) on the ABC Television Network.

The hour, which is an update from a September 2009 report, includes an exclusive interview with Paolilla's parents and the victims' families, as well as a new interview with Police Sgt. Brian Harris.

"20/20" is anchored by Elizabeth Vargas. David Sloan is executive producer.