No one could have expected, or even imagined, the nightmare that blew through the halls of Columbine High School in Littleton, Colorado on Tuesday, when at least two laughing killers, both students, made their way through the building armed with sawed-off shotguns, a rifle, a pistol, and more than 30 homemade bombs.

When the shooting was over, 12 students and one teacher were dead, 23 students were wounded, and two alleged murderers, members of a school clique called the "Trenchcoat Mafia," had turned their guns on themselves.

MTV News' Chris Connelly was on the scene to hear firsthand accounts from the teenagers who lived through the seige at Columbine High.

First came the harrowing stories of survival: by fate, by chance, and by the whim of at least two ecstatic killers.

"They were just like, 'We've waited to do this our whole lives!'" Crystal, a 17-year-old Columbine survivor, told us. "And then they'd shoot people, and then they'd yell, 'Yay!' You know? Like it was like they were excited. They were like, 'Who's ready to die? Who's next?'"

"They were just throwing bombs and shooting," said Bill, 16. "I know they saw us. They had to, 'cause the girl I was holding on to had some shotgun shells dropped on her."

"The shotgun just sounded like a cannon," added Craig, 17.

Toward the end of their spree, the killers would find themselves face-to-face with Cassie Bernall, a junior who not long ago had herself been a school outcast.

"She knew what it was like to have no friends, and to not even have people come up and say as much as 'hello,'" recalled Shauna, 19, who knew Bernall.

But, say her friends, Cassie's parents intervened. She joined a church group and became a born-again Christian.

"From that point on, she was the most gentle, loving, kind and quiet-spirited person I had ever met in my life," said Shauna.

On April 20, Cassie was in the library. That's where, her friends have been told, Cassie was offered a deadly choice between her life and her faith.

"They said, 'Do you believe in God?'" Craig recounted. "And she said, 'yes.' And that was Cassie. It was Cassie, that's who it was, you know. And so we know... we know how she ended her life, you know. A martyr. As Shauna said, she died for what she believed."

For the students at Columbine High School, getting through the days ahead will mean staying close to those they love.

"Friends are very helpful, because they understand what you're going though," offered Emily, 17. "But at the same time, it's one time that you really want to be near your family. Because all these kids woke up yesterday, went to school, and a lot of 'em will never see their parents again."