It started as a report of a possible fire Thursday morning at a Gwinnett County apartment complex, but firefighters quickly made a gruesome discovery: A boy, believed to be 6 years old, had been stabbed multiple times and died from his injuries, police said.

Firefighters responded to The Vine apartments at 4900 Springs Lane in Peachtree Corners shortly before 8 a.m., investigators said. Crews didn’t see flames, but they heard alarms from a first-floor unit and entered it, a Gwinnett police spokeswoman said. Inside, the boy was found unresponsive.

The child, whose name was not released, was taken to a Children’s Healthcare of Atlanta hospital but did not survive.

“What began as an apartment fire is now a criminal investigation,” Gwinnett police Sgt. Michele Pihera said.

Firefighters extinguished flames in two bedrooms of the apartment, according to Gwinnett fire Lt. Andy Lane. He declined to say where the boy was located. The child was the only person inside at the time.

Arson investigators are working with officers to determine the cause of the fires, Lane said.

Around 9:15 a.m., officers located a woman who appeared to be hiding behind a building at the apartment complex, according to Pihera. She was wet and not wearing shoes, but had on one sock, Pihera said.

The woman was not identified, but is believed to be related to the boy and also lived in the unit, according to police. She was taken to a hospital and was expected to be questioned by investigators, Pihera said.

The investigation continued Thursday afternoon. Chaplains were available to assist any investigators involved in the case, Pihera said.

The child’s death comes three days after a 7-year-old boy was killed in what investigators believe was a murder-suicide in DeKalb County. Officers were called at 3:15 p.m. Monday to a home in the 3100 block of Briarcliff Road, according to a spokesperson for DeKalb police. There, investigators found two adults and a child dead, according to police.

Anyone with information on the Gwinnett case is asked to contact detectives at 770-513-5300. To remain anonymous, tipsters should contact Crime Stoppers at 404.577.TIPS (8477) or visit www.stopcrimeATL.com.