Somer Thompson, right, is seen in this undated family photo.
Oct. 21: Diena Thompson, mother of 7 year old Somer Thompson, speaks during a morning television news conference asking for help in Orange Park, Fla.
An undated family photo shows Somer Thompson, a missing seven-year old-girl from the Grove Park neighborhood of Orange Park, Fla.
Photo of Somer Thompson.
Florida police have tentatively identified a child's body found in a landfill as that of a 7-year-old girl who vanished while walking home from school on Monday.
Sheriff Rick Beseler said Thursday that Somer Thompson was identified based on clothing and a birthmark that matched an "odd-shaped" mark on her left shin.
The little girl was found partially covered in a Georgia landfill near the Florida state line, after investigators followed garbage trucks leaving the neighborhood where Somer disappeared.
Beseler told an early-morning news conference that investigators searched through 100 tons of garbage before finding the missing child. Authorities were holding another news conference Thursday at 4 p.m.
The sheriff said he had told the girl's mother to prepare for the worst, and called her Wednesday night after receiving the news that the body was Somer's.
"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."
Somer's father, Samuel Thompson, gave an emotional interview Wednesday before the remains were identified saying he knew it was probably his daughter in the landfill.
"I'm so angry. I'm so hurt," Thompson, of Graham, N.C., told the Florida Times-Union as he wept. "My baby daughter laying in trash. Discarded like a piece of trash. God help the sons of bitches who hurt my daughter. They better find them."
The cause of death hasn't yet been released, but the Georgia Bureau of Investigation planned an autopsy Thursday in Savannah.
"We hope to learn the cause and manner of the death that will assist us in the criminal investigation we are actively undertaking at this time," Beseler said. "The early discovery will be tremendously helpful in this investigation to help find the person or people responsible for the death of this beautiful child."
Beseler said he still fears for the community until a suspect is caught.
"This is a heinous crime that's been committed," the sheriff said. "And we're going to work as hard as we can to make this community safe."
He 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.
A crowd of about 150 people, some crying, gathered across the street from Somer's home on Wednesday, many clutching their children tightly. Others placed flowers under a tree.
"We are all devastated," said Tonya Jennings, a grandmother who lived three doors away and often saw the girl and her siblings come home from school. "I knew her."
Somer vanished on her mile-long walk home from school Monday in Orange Park, a suburb of Jacksonville, after she squabbled with another child and her sister told her to stop. Somer got upset, walked ahead of the group and wasn't seen again.
The area where the girl disappeared is a heavily populated residential neighborhood. Authorities launched a countywide search involving helicopters, dogs and volunteers walking arm-to-arm through wooded areas.
Somer's mother, Diena Thompson, said earlier Wednesday that she assumed someone had her daughter. Police suspected foul play after first investigating whether she had gotten lost or fell on the walk home.
An FBI forensic unit is helping process evidence from the landfill in Folkston, Ga., located about 48 miles from where the girl disappeared.
People are encouraged to call the tip line at (877) 227-6911 with any additional tips and information that may help the murder investigation.
The Associated Press contributed to this report.