After 7-year-old Somer Thompson vanished on her way home from school, investigators tailed nine garbage trucks from her neighborhood to a Georgia landfill nearly 50 miles away, then picked through the trash as each rig spilled its load.

They sorted through more than 225 tons of garbage before their worst fears were realized: Sticking out of the rubbish were a child's lifeless legs.

Sheriff Rick Beseler said the quick discovery of Somer's body on Wednesday, two days after she disappeared, may have saved precious evidence that could lead to her killer.

"Had we not done this tactic, I believe that body would have been buried beneath hundreds of tons of debris, probably would have gone undiscovered forever," he said Thursday.

An autopsy to establish the cause of death was performed Thursday, but authorities would not disclose their findings. At a news conference, Beseler would not say if Somer had been sexually assaulted or answer other questions about the condition of the body.

"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."

LIVESHOTS: Police ID Body as Missing Florida Girl

SLIDESHOW: Somer Thompson Disappears on Walk Home From School

Searching landfills is common when children disappear, but it is unusual to try to zero in on them more efficiently by tracking a neighborhood's garbage trucks, said Ernie Allen, president of the National Center for Missing and Exploited Children.

"Time is the enemy in these cases and the sheriff used every resource," Allen said.

The sheriff said police have questioned more than 155 registered sex offenders in the area so far. State online records show 88 sex offenders live in Orange Park, a Jacksonville suburb of about 9,000 people just south of Jacksonville Naval Air Station.

Beseler would not say whether investigators believe the crime was committed by more than one person.

Somer's father and other family members were "torn up" upon hearing the news, aunt Laura Holt said.

As for the killer or killers, "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?"

The girl disappeared in a heavily populated residential area about a mile from a stretch of fast-food restaurants and other businesses. Investigators will presumably try to pinpoint the trash bin or garbage can where she was dumped, based on the trash around her and the truck's pickup route.

Tuesday was trash day in Somer's neighborhood, and it was Detective Bruce Owens' idea to track the garbage trucks to the landfill they use in Folkston, Ga., 48 miles way.

"At that time I realized that this is probably not going to turn out good," the 10-year veteran of the Clay County Sheriff's Office told The Florida Times-Union. But he said he had been expecting to find perhaps a backpack or a piece of clothing, not a body.

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

"Needless to say, she was absolutely devastated," Beseler 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 vanished on Monday during her mile-long walk home from school. Authorities said she squabbled with another child and walked ahead of the group. She was last seen outside a vacant house that was on her route home, sheriff's spokeswoman Mary Justino said. Investigators are examining the house for evidence, Justino said.

On Thursday, flowers and dozens of teddy bears were heaped around an oak tree across the street from Somer's home where about 200 people gathered for a candlelight vigil in front of the family's home just after sundown.

Diena Thompson came out to thank the group who sang "Amazing Grace" and "You Are My Sunshine," then recited the Lord's Prayer.

"I wish I could hug every one of you," Thompson said. "I love every one of you."

Neighbor Carter Beukema shouted his comments about if the accused killer goes to trial: "I hope I'm on the jury. He will pay."

Somer "was always happy unless she couldn't find anyone to play with," neighbor Robert Ocain said. "She trusted anybody. Honestly, I think all the kids around here do."

At the tree, Catherine Sullivan held her teary-eyed 5-year-old daughter, Nya Frederick. They drove to the Thompsons' neighborhood from Jacksonville because Sullivan wanted to show her child the dangers of being too friendly with strangers.

"She seemed to understand when I explained to her her mommy wouldn't see her anymore," the mother said.

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