There was nothing that immediately indicated the remains were Caylee's. But Orange County Sheriff Kevin Beary said his investigators and the FBI would work around the clock and through the weekend to identify the child.
"Now the investigation continues," Beary said. "There is a lot of lab work to do. There is a lot of DNA work to do. There is a lot of crime scene work to do."
Caylee's mother, 22-year-old /*Casey Anthony*/, was indicted in October on first-degree murder and other charges, even without a body. She has insisted that she left the girl with a baby sitter in June, but she didn't report her missing until July.
For the past several months, Anthony's family, police and volunteers from around the country have searched for the little girl.
A member of EquuSearch - one of the volunteer groups - said they did not check the location in early September because it was submerged in water. When they returned in November, the site had been fenced off.
EquuSearch volunteer Deborah Smith said she believes the remains belong to Caylee.
"I'm glad she was found before Christmas so they can give her a proper burial," Smith said.
Allen Moore, a spokesman for the Orange County jail, said Casey Anthony was told about the discovery. She was placed under psychological observation, not suicide watch, and remains under protective custody. Her attorney, Jose Baez, was at the jail for about 90 minutes Thursday.
Forensic experts said it was harder for investigators to identify a child's remains than an adult's, but they would have a few methods to pursue.
Medical examiners would probably look at photos of the child along with the skull, hoping to make a bone structure comparison, said Dr. Lee Jantz, coordinator of the forensic anthropology center at the University of Tennessee.
Dr. Bill Manion, a pathologist and an assistant medical examiner for Burlington County, N.J., said DNA testing could determine an identification even without other DNA from the victim, "as long as we know who the parents are or siblings."
By early Thursday afternoon, dozens of reporters, police and onlookers had gathered in the pouring rain near where the remains were found. One man walked up and placed a flower-covered cross at the scene. Another man openly sobbed. An elementary school at the end of the street released students out through a back pedestrian exit, steering them away from the frantic scene.
Sheriff's spokesman Angelo Nieves said officials told Caylee's grandparents about the find, but refused to discuss whether the remains were Caylee's. But Nieves also said there were no other similar missing-children cases in the area.
The child's grandmother first called authorities in July to say she hadn't seen Caylee for a month and her daughter's car smelled like death.
Police immediately interviewed Anthony and soon said everything she told them about her daughter's whereabouts was false. The baby sitter was nonexistent and the apartment where Anthony said she had last seen Caylee had been empty for months. Anthony also lied about where she worked.
Other troubling details emerged as the case picked up national media attention: Photos surfaced of Anthony partying after her daughter went missing. Friends said she was a habitual liar, but also a good mother.
Last month, the Orange County State Attorney turned over almost 800 pages of documents showing someone used the Anthonys' home computer to do Internet searches for terms like "neck breaking" and "household weapons."
In mid-March, someone searched Google and Wikipedia for peroxide, shovels, acetone, alcohol and chloroform. Traces of chloroform, which is used to induce unconsciousness and a component of human decomposition, were found in the trunk of Casey Anthony's car during forensic testing, the documents say.
Last week, prosecutors announced they would not pursue the death penalty for Anthony. Earlier Thursday, before the remains were discovered, a judge had delayed her trial from January to March.
A spokeswoman with the state attorney's office said it would reserve comment until the investigation was complete. Messages left with Caylee Anthony's grandparents and with Casey Anthony's lawyer were not immediately returned.
Associated Press Writers Tamara Lush, Suzette Laboy, Damian Grass, Sarah Larimer and Antonio Gonzalez in Miami contributed to this report.