A man was found dead Thursday in burning apartment in suburban Midlothian, and investigators are trying to find out how it started.

The dead man, believed to be in his 20s, was not identified by authorities by Thursday night. His grieving family members on the scene declined to comment.

Midlothian firefighters were called about 10:30 a.m. to a second-floor fire in the 12-unit Amberley Courts Apartments in the 3600 block of West 147th Street, according to Deputy Police Chief Steve Zamiar.

It is believed the victim was the sole tenant and was alone at the time of the fire, he said.

Police were working with the Midlothian Fire Department, the state fire marshal’s office and the Cook County evidence technician team to determine how and where the fire started, Zamiar said.

Asked if the fire was suspicious, Zamiar said, “We just don’t know.”

There was extensive damage inside the apartment and water damage to two apartments below, Zamiar said.