ORANGE PARK, Fla. (AP) — Authorities believe a body found in a landfill is that of 7-year-old Somer Thompson, a north Florida girl who disappeared on her walk home from school, the sheriff in charge of the case said Thursday.

Sheriff Rick Beseler said the tentative identification was based on clothing and on a birthmark that matched the girl’s.

Detectives spotted the legs first and found the body partially covered by garbage Wednesday in a Georgia landfill near the Florida state line, after investigators followed garbage trucks leaving the neighborhood where the child disappeared Monday.

Somer’s father and other family members were “torn up” after hearing the news, aunt Laura Holt said. She hopes authorities will find her niece’s killer.

“I don’t think they deserve to live,” Holt said. “I don’t think there’s anything worse that a person can do — to kill a child and dump her in the dump like a piece of trash?”

Beseler wouldn’t talk about what evidence police have recovered, or whether investigators believe the crime was committed by one or more people. He said police have questioned more than 70 registered sex offenders in the area, and that process was continuing. Florida Department of Law Enforcement records show 161 offenders live in a 5-mile radius of Somer’s home.

“I fear for our community until we bring this person in. This is a heinous crime that’s been committed,” Beseler said. “And we’re going to work as hard as we can to make this community safe.”

The sheriff said he told the girl’s mother to prepare for the worst, and called her after receiving the news Wednesday night.

“Needless to say, she was absolutely 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 credited one of his detectives with suggesting on Tuesday that the landfill should be checked. Trucks were scheduled to pick up garbage in Orange Park on Tuesday morning. He said detectives were told to go through the debris looking for evidence as the trucks brought it in.

“Had we not done that, tons of garbage would have been distributed over the top of the body, and it likely would have never been found,” he told ABC’s “Good Morning America.”

Two deputies stood guard at mother Diena Thompson’s home early Thursday morning. It appeared to be full of supporters. An oak tree across the street was decorated with flowers, candles and pictures of Somer.

“This has been so unreal for the neighborhood,” said Sharon Galloway, who lives across the street from the Thompsons. “I just hope they get that son of a gun and tie him up by his short hairs.”

An FBI forensic unit is helping process evidence from the landfill in Folkston, Ga., about 48 miles from where the girl disappeared.

The Georgia Bureau of Investigation planned an autopsy Thursday in Savannah.

Somer vanished on her mile-long walk home from school in Orange Park. She was squabbling with another child, and her sister told her to stop. The girl got upset, walked ahead of the group and wasn’t seen again.

Authorities launched a countywide search involving helicopters, dogs and volunteers walking arm-to-arm through wooded areas.

Orange Park is a suburb of Jacksonville just south of Jacksonville Naval Air Station. The area where the girl disappeared is a heavily populated residential area with homes, apartment complexes and condominiums.

The girl’s father, Sam Thompson, lives in Graham, N.C.