"It's worse than losing a child to a car wreck," said family friend Dawn Barrs, whose sons also attended Walton High and knew Burk. "It's just a sincere tragedy --- a nightmare."
Police had made no arrests as of late Wednesday afternoon, Hardin said.
Walton student Greg Greene met Burk in math class when he was a freshman.
"She was the first older person ever to talk to me and be a friend of mine," he said. She was "probably the greatest girl I know."
"I just remember her as always having a ton of friends," he said.
She played lacrosse, he said. He last talked to her about a month ago.
"She told me how she didn't like Auburn that much," he said. "She missed high school and she missed all of her friends in high school."
He found out about her death when he was talking to a counselor and another student who had just learned of Burk's death came in crying.
"I didn't really know how to react," he said. "It's hard to think of someone getting murdered."
Word about her death filtered out Wednesday at Walton.
Senior Monique Osigbeme heard the news as she was on her way to compete in a track meet.
"She was always smiling, always laughing and happy," she said. "She had a really nice smile and really pretty brown hair. Oh my God, that's really sad."
Principal Tom Higgins said, "She was a great leader, a great kid. She was a very, very good student."
Barrs, who went on a spring break trip to Panama City, Fla., with Burk and other parents and students last year, said Burk stood out from other kids her own age because she seemed more mature.
"She was level-headed and a very responsible student," Barrs said.
Barrs said Burk and her longtime boyfriend attended Auburn together, and that Burk's older sister also is a student at Auburn.
Family members told Barr that the couple were together about two hours before Burk's killing, but Burk went to the library to study with friends "and never made it there," Barrs said.
Officials at Auburn, which has many metro Atlantans among its nearly 25,000 students, issued a statement saying there is "no indication of additional danger to campus or student safety."
Burk's sorority also released a statement that was posted on the university's Web site.
"Considering the unexpected and disturbing nature of the situation, the women of Delta Gamma have reacted with immense concern," the statement read. "... Delta Gammas across the country offer hope and friendship to Lauren's family and all who have been affected by this tragedy."
Staff writer Mike Morris contributed to this article.