Georgia Bureau of Investigation spokesman John Bankhead said that "everything points to it being" Jorelys Rivera of Canton. Bankhead said officials were awaiting results of an autopsy to confirm the identity and a cause of death.
Bankhead told The Associated Press the body appeared to have been severely beaten and sexually assaulted. He said the girl's mother had been notified.
No suspects were in custody as of Monday night, authorities said.
The girl's mother returned to the apartment complex early Monday evening. Crying, the woman entered the family's apartment without speaking to reporters and a family friend asked for privacy.
The child was last seen around 5 p.m. Friday at the River Ridge apartments in Canton, about 40 miles north of Atlanta, Canton police Detective Candy Worthy said. The girl was at the playground with a teenage baby sitter. The girl had gone back to her apartment to get sodas for friends when she disappeared, authorities said.
Authorities brought in a specialized team of law officers trained to handle child abductions. The body was located about 1 p.m. Monday.
Canton emergency management director Jeff Hall said authorities had not searched the trash container until Monday because it was a large garbage compacting bin that needed to be moved offsite so they could go through it.
Bankhead, the GBI spokesman, said investigators believe the girl was killed at the apartment complex and her body left in the trash bin. Yellow crime scene tape blocked off the wooded area behind the girl's apartment building.
Authorities planned to provide an update on the investigation Tuesday morning.
Maria Rodriguez works with Rivera's mother at a nearby poultry plant and used to live in the same complex.
"She was a very sweet girl," Rodriguez said, crying as she held her 4-year-old daughter. "She was the type of little girl who likes her presence to be known. It's just so sad."
Rodriguez said Rivera's mother worked the graveyard shift. Police have since removed two other young children from the Rivera home over "concern about the supervision of Jorelys," said Lt. Jay Baker with the Cherokee County Sheriff's Department.
Maria Faustino, who also used to live in the apartment complex, said she always felt safe there.
"This place is small and everybody knows everybody," said Faustino, who has a young son. "You wouldn't have thought something like this would have happened there."
A schoolmate who lived in a neighboring complex, 8-year-old Ashley Rosalez, said Rivera was very talkative and that she would play on all the playgrounds in nearby apartment complexes.
Another neighbor, Nancy Hudgins, who lives next to the trash bin where the body was found, said the little girl liked to swim at the pool in the complex with her siblings and loved to pet animals that lived in the area.
She said the Rivera family was "mostly quiet" and kept to itself.
Officers were checking with sex offenders in the area, an effort that will possibly broaden as the investigation continues, Bankhead said.
There are 73 registered sex offenders living in Canton, according to state records online.
Authorities did not issue a Levi's Call - the state's version of an Amber Alert - because officers didn't have any information about the girl's abductor, which is a requirement for issuing such an alert.
Michelle Mercier, who lives across the street from the complex, brought a bouquet of yellow, pink and purple flowers to the playground where Jorelys was last seen. Soon after, neighbors and community members flocked to the playground Monday to leave flowers and stuffed animals and held a candlelight vigil there.
"I wanted everybody to know I'm thinking of her, this precious little girl who is no longer with us," Mercier said.