Connie Chung Interviews School Shooter

April 13 -- Fourteen-year-old Elizabeth Bush hung posters of Mother Teresa and Martin Luther King Jr. in her room. She thought perhaps she would become a nun one day.

But instead of finishing high school, she now faces spending the rest of her adolescence locked in a juvenile facility.

On March 7, Bush walked into her school cafeteria with her father's gun and started shooting. "There was a deep part of me that just exploded," Bush tells Connie Chung in a 20/20 interview, "I'm not normally like that."

Her only victim was 13-year-old Kimberly Marchese, who was shot in the shoulder. Though it will be a long time before Marchese has full use of her arm again, she says it didn't hurt when her classmate shot her. "It was like a dead person's arm attached to me," she remembers.

What would push Bush, a seemingly shy girl, to the brink? For years she left a trail of clues but her parents, teachers, counselors and friends did not pick up on the warning signs.

Bush grew up in a loving family and had no history of violence. The serious, introverted, deeply religious girl was, in fact, unusually caring. "We used to tell each other how lucky we were to have a child with such a good heart," says Bush's father.

Excruciating Depression

Bush was clearly different from the other kids. She was a nonconformist and by the time she entered junior high school, they began to make fun of her. She became depressed and frequently skipped school without her parents' knowledge. As her depression worsened, she began to cut herself with a razor blade and often contemplated suicide.

Increasingly concerned, her parents transferred Bush to Bishop Neuman High School, a small parochial school. It was Bush's chance for a fresh start.

School records indicate Bush was "depressed," "withdrawn," and "very defensive if someone gets too close." Teachers said she was "paranoid and felt persecuted." And the teasing continued. Marchese, who was one of Bush's few friends, says, "They would say that she was like a freak or she was weird or she was like messed up."