Jorelys Rivera was only 7, but she stood out for her bubbly demeanor in the north Georgia apartment complex where she lived.

Investigators said they believe one of those who noticed the girl -- someone who either lived in the modern, sprawling complex or had regular access to the apartments -- may be her killer. Rivera was abducted near a playground at the complex, taken to a vacant apartment, and sexually assaulted before she was stabbed and beaten to death and her body placed in a trash bin, authorities said Tuesday.

"This was a very calculated and planned crime," Georgia Bureau of Investigation Director Vernon Keenan said.

Police still have no suspects in the case.

Keenan on Tuesday released autopsy results and new details in the killing of Rivera of Canton, who was last seen Friday evening. The autopsy showed the girl died of blunt force trauma 60 to 90 minutes after she disappeared, though police did not give a time of death.

He said evidence collected from the child's body and the vacant apartment are being tested. Investigators hope to have preliminary DNA results later Tuesday.

Rivera's family lives in a community about 40 miles north of Atlanta with a swimming pool, club house and two playgrounds. The complex is a series of three-story apartment buildings with meticulous landscaping, surrounded by an idyllic backdrop of trees and hills.

On Monday, many apartments were decked out in Christmas lights and decorations as neighbors watched GBI agents search the grounds for more clues in the child's killing. Neighbors repeatedly said parents felt safe letting their children roam freely in the complex because it's surrounded by a fence and was a quiet place to live.

But police have identified and interviewed several sex offenders living at the complex, Keenan said. He added, "We have no reason to believe, at this point, that sex offenders are involved."

Keenan said investigators have received numerous tips from the public and said valuable evidence has come from apartment complex residents.

As details of the crime came out, residents interviewed Tuesday acknowledged they were worried.

"I'm very concerned," said Drew Baucom, 17." It makes me feel like my home life is violated, that I can't trust somebody walking around that you think you may know, but you really don't. It just worries me that something else will happen like this."

Police said the girl was last seen around 5 p.m. Friday at the River Ridge apartments in Canton.

She was at a playground within the apartment community with a teenage baby sitter. The girl had left the playground to return to her apartment to get drinks for her friends when she disappeared.

About 65 local, state and federal investigators are working on the case and several hundred interviews have been conducted, authorities said.

Jeremy Gibson, 24-year-old resident of the apartment community, said he is concerned about the safety of all the children who live there.

"Every day children play out here," he said. "It's starting to become a dangerous place for them. If it's happened to one little girl already, it could happen to someone else. I hope they catch whoever did it soon."

Maria Rodriguez, a former resident of the apartment complex, said she works with the victim's mother at a nearby poultry plant.

"She was a very sweet girl," Rodriguez said Monday, crying as she held her own 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 the girl's mother worked a 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.

Baker said no charges were expected against the mother or the babysitter.

A prayer vigil was held late Monday at the playground, where people left flowers, balloons and stuffed animals at a makeshift memorial.

A $15,000 reward has been issued for information leading to the arrest and conviction of the girl's killer.

"We're following up on every single tip," Baker said.

This is based on a story by The Associated Press.

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino