A 15-year-old Chicago boy found dead in a burning trash container last month was alive when the fire was started, officials determined.

Demetrius Griffin, Jr. died of “thermal injuries due to incendiary fire in garbage can,” according to the Cook County Medical Examiner’s Office.

The manner of death was ruled a homicide, KTLA sister station WGN reported.

Griffin, a freshman at Steinmetz High School on Chicago’s Northwest Side, was found burned beyond recognition in an alley in mid-September.

Neighbors, friends and family gathered days after the slain teen was identified to hold a vigil in the Austin neighborhood where he was found.

Griffin’s only sibling, older sister, Bre Melchor and Polynesia Sykes attended the vigil and pleaded for peace and information.

“I need your help, please,”Sykes. “They’re killing our kids. You know who you are. Turn yourself in.”

Sykes said she knew something was wrong when he missed curfew the night before he was found – it was something she says he never did. Demetrius, who had just started high school before he was killed, had hopes of joining the swim team.

A reward of $7,500 is being offered for information leading to the arrest of Griffin’s killer. Police said whoever set the fire may also have suffered burns.

So far, no arrests have been made.

This video originally aired Sep. 20, 2016: