(CNN) -- The news was devastating, the aftermath surreal.
Diena Thompson clutched a tissue in her right hand, frequently wiping her eyes as she told reporters that she couldn't believe it was her daughter whose body was found in a Georgia landfill. Her visage revealed the weight of grief and a yearning for justice.
Standing outside her home in Orange Park, Florida, Thompson looked into the camera and, with her voice cracking, sent out a stern warning to her daughter's killer.
"I want you to know that I will not sleep until this person is found. I hope they get you, and I hope they make you pay for a long, long time. You don't take from somebody. You didn't just take her from me. You took her from my family; you took her from all these people. And you don't do this to a little baby and put my baby in the trash like she's nothing. That's not OK, this is not OK."
The body of her daughter, 7-year-old Somer Thompson, was found in a South Georgia landfill, Clay County, Florida, Sheriff Rick Beseler said Thursday.
On Monday, Somer became separated from her siblings and schoolmates on her way home from school in Orange Park.
She was seen in a fight at school before disappearing, according to a police report Thursday. Her 10-year-old sister told police that Somer had gotten into a fight with another girl at school earlier in the day.
The sister said she brought up the fight while she and her brother walked Somer home from school, and that Somer ran off from them, apparently upset. The sister said she lost sight of Somer in a group of other kids leaving the school, according to the police report.
A medical examiner in Savannah, Georgia, used dental records to identify the body positively as Somer's, said Clay County Sheriff's Office spokeswoman Mary Justino.
The sheriff told the girl's mother Wednesday night that her daughter had been identified. Thompson was devastated, he said.
"It was the hardest phone call I've ever had to make in my life, and I hope I never have to make another one like that," Beseler said at a Thursday news conference.
Authorities are turning their full attention to finding the child's killer.
The landfill where her body was found is near Folkston, Georgia, 55 miles north of where the girl became separated from her schoolmates.
Authorities will work to pinpoint where the garbage load that contained the girl's body came from, Beseler said. The garbage brought into that part of the landfill was collected in the Orange Park area, he has said, noting that authorities routinely search garbage when a missing person case has been initiated.
The investigation has turned into a murder probe.
"There is a child killer on the loose," the sheriff said. "I fear for our community until we bring this person in."
Investigators in Georgia are combing through a "tremendous mountain" of garbage at the landfill, searching for clues, said Justino, the sheriff's office spokeswoman, on Friday.
Some possible evidence has been removed from the landfill, but authorities won't describe what they found, Justino said. Police have no suspects, she said.
She said other law enforcement teams are focusing on the locale where the child apparently was last seen. Justino said witnesses, including some children, saw her on the sidewalk in front of a vacant house under renovation after a fire.
"Since Monday, we have been trying to figure out who frequents that area," including anyone working on the home, she said.
Rewards totaling $30,000 have been offered for information leading to the arrest and conviction of whoever is responsible.
Justino said of the 810 leads called in to a tip line, 231 were being actively pursued by a group of 50 detectives.
Overnight, detectives finished interviewing 90 registered sex offenders or predators within a five-mile radius of the Thompson home, the spokeswoman said.
Somer's family was making funeral arrangements Friday, Justino said, and many in the community had offered to help financially.
"There has been an outpouring of support from the community," she said.
CNN's Maria P. White contributed to this report.