Police in Florida urged the public Wednesday to be suspicious of changes in behavior and appearance among the people they know — because one of them could be 7-year-old Somer Thompson's killer.

Somer's body was found buried under a mound of garbage in a Georgia landfill on Oct. 21, two days after she disappeared as she was walking home from school in Orange Park, Fla. The little girl was buried on Tuesday.

"Yesterday was about Somer Thompson," Clay County, Fla., Sheriff Rick Beseler said during a brief press conference Wednesday. "Today is about her killer."

Beseler, who gave a prepared statement and took no questions, said he needed help finding Somer's murderer from "certain people" who live nearby.

"We have reason to believe there are individuals in the community who have information pertinent to this case who have not come forward ... people who may know or associate with the offender," the sheriff said.

SLIDESHOW: Somer Thompson Murder

He asked the public to be on the lookout for friends, relatives and acquaintances who have shown changes in their patterns or behavior since Somer was killed.

People who have suddenly left the area, missed work, suffered unexplained injuries or changed their appearance — by shaving or growing head or facial hair, for example — should arouse suspicion, Beseler said.

He also encouraged people in the community to identify anyone who has abruptly hidden or sold a car, acted increasingly nervous or irritable, shown unusual interest in the case or altered his or her alcohol consumption or sleep patterns.

The Clay County Sheriff's Office has investigated about 1,700 leads, but it has not named any suspects or people of interest.

Authorities say they have ruled out all 161 registered sex offenders who live within a 5-mile radius of Somer's home.

The little girl vanished on her way home from her elementary school Oct. 19 in a heavily populated residential neighborhood, after she got upset during an argument with other children and ran ahead of the group.

She was last seen walking along the sidewalk in front of a vacant house. Authorities have been searching for anyone who saw the girl after that.

So far, no witnesses have come forward to say they saw Somer being attacked or abducted.

Investigators have sifted through evidence from the empty house and the Georgia landfill where her body was found.

Her mother Diena Thompson has appeared several times on TV warning her daughter's killer that "we'll get you" and pleading for any clues leading to a suspect's capture.

Anyone with any information or tips is asked to call 1-877-277-6911.

The Associated Press contributed to this report.