Authorities said Friday that the preliminary autopsy report on a newborn infant found dead in the woods near Mableton shows no signs of trauma, although the cause of death is still unclear.

The infant’s mother, a 13-year-old Cobb County girl, is being charged as an adult in the death of the baby, and police are investigating other youths who may have been involved in leaving the body covered by leaves in a field behind an apartment complex.

The mother was arrested Thursday at her home and charged with felony first-degree cruelty to a child, felony murder – causing death in the commission of a felony – and concealing a death, Cobb County police spokesman Officer Mike Bowman said.

“This is a tragedy,” he told AM 750 and 95.5 FM News/Talk WSB. “You’ve got a 13-year-old child giving birth and then disposing of a baby. It’s very traumatic for all people involved.”

Cobb County Police spokesman Sgt. Dana Pierce told the Atlanta Journal-Constitution the baby was born just after midnight Tuesday morning, in the teen’s room adjacent to her parents’ room.

“The girl’s parents were asleep in the bedroom next door during the birth,” Pierce said. “We believe … that she discovered the baby deceased when she woke up (later) that Tuesday morning.”

The Cobb County Medical Examiner’s office continues to investigate the cause of death and whether the infant was stillborn, Pierce said.

More details from the autopsy will likely be available early next week, police say.

The teen remains in police custody, although it is unclear where she is being held.

From the time of the infant’s death, police said there were other children who learned about the death and others involved in the apparent plot to dispose of the baby’s body.

“In that afternoon, after school, there were several other youth that participated in placing the body in a shoebox and placing it under those leaves,” Pierce said.

He said the 14-year-old father of the child has not been charged but is among those being investigated.

“One of those children became very emotional and felt guilty about what had been done,” Pierce said. “He reported it to school authorities, who reported it to school police that in turn reported it to Cobb police.”

Police investigators found the infant’s body around 4:15 p.m. Wednesday, police said, and turned the body over the medical examiners.

It is unclear to investigators whether the 13-year-old girl’s parents knew she was pregnant, but police say they are not being charged.

Georgia has a Safe Haven law which allows mothers to leave newborn babies with an employee of a medical facility without facing criminal charges.

— Staff reporter Alexis Stevens contributed to this article.