CNN: The body of a small child found in a south Georgia landfill has been identified as that of a missing 7-year-old Florida girl, Clay County, Florida, Sheriff Rick Beseler said Thursday morning.

John Bankhead of the Georgia Bureau of Investigation told CNN the state medical examiner will positively determine whether the body belongs to Somer Thompson, who went missing earlier this week. An autopsy will be conducted in Savannah, Georgia.

The preliminary identification was based on the girl's clothing and a birthmark, Beseler said.

The landfill is near Folkston, Georgia, 55 miles north of where the girl became separated from her schoolmates on her way home from school in Orange Park, Florida, on Monday.

The sheriff told the girl's mother Wednesday night that her daughter had been identified. The mother, he said, was devastated.

"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 morning news conference.

Authorities will work to pinpoint where the garbage load that contained the girl's body came from, Beseler said. The garbage that was brought into that part of the landfill was collected in the Orange Park area, Beseler had said Wednesday, noting that authorities routinely search garbage when a missing person case has been initiated.

The investigation has now 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."

Rewards totaling $30,000 have been offered for information leading to the arrest and conviction of whoever is responsible.

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