Florida Department of Law Enforcement investigators look for clues Thursday in the Somer Thompson murder investigation in a dumpster near a vacant house in Orange Park, Fla. A body found under trash in a landfill is that of 7-year-old Somer Thompson, a north Florida girl who vanished Monday on her walk home from school, authorities said Thursday.

Orange Park, Fla. ? 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.”

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 away.

“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.