According to an incident report from the Greene County Sheriff's Department, an ambulance responded to an address on Fairview Road in Afton on September 17.
Eight-month-old Abby Leann Jennings of Greene County was having trouble breathing and her pupils were unresponsive.
The report said medical staff found various stages of bruising and a possible bite mark on the infant's body. A detective responded to Laughlin Memorial Hospital in Greeneville to investigate.
The infant was later transported to a hospital in Johnson City where she died on September 19.
District Attorney General Berkeley Bell said Jennings' death is now being treated as a homicide.
Although an autopsy is not complete, Bell said a forensic pathologist found the baby died from traumatic injuries.
"The child suffered from other injuries," Bell explained. "But, the lethal injury was to the head, the brain."
The Tennessee Bureau of Investigations is helping the District Attorney's office with the investigation.
District Attorney Bell said there are suspects in the case. Bell plans to take his findings before a grand jury when his investigation is complete.
The incident report shows the address where Jennings was picked up by the ambulance is not the child's home.