Georgia Bureau of Investigation Director Vernon Keenan released autopsy results and new details on the case at a news conference Tuesday morning in the north Georgia town of Canton.
Jorelys Rivera, 7, died of blunt force trauma to her head, results of an autopsy showed.
Keenan called the crime a "very horrific and brutal murder."
Investigators feel strongly the killer lives in the apartment complex or has regular access it, Keenan said.
"Investigators feel very strongly that the killer of the child resides in the apartment complex or has regular access to the apartment complex," Keenan said. "So our efforts at this point are concentrated in that area."
No suspects are in custody. Investigators say they're continuing to pursue leads, and a $15,000 reward has been issued.
Keenan also said that evidence collected from the child's body and the apartment are being tested. He said they hoped to have preliminary DNA results by later Tuesday.
Police say Jorelys was last seen around 5 p.m. Friday at the River Ridge apartments in Canton, about 40 miles north of Atlanta.
The girl was at the apartment complex playground with a teenage baby sitter. She had gone back to her apartment to get sodas for friends when she disappeared, authorities said.
Authorities are receiving numerous calls from residents at the apartment complex, Cherokee County sheriff's Lt. Jay Baker said Tuesday.
"We're following up on every single tip," he said.
No suspects are in custody in the death.
Jorelys 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.
Michelle Mercier, who lives across the street from the apartment 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.