CHICAGO (NewsNation Now) — An off-duty Chicago police officer fatally shot another off-duty officer Tuesday night, according to the Chicago Fire Department.

Sources told NewsNation affiliate WGN that the incident was domestic and involved an off-duty female officer and an off-duty male officer.

According to multiple sources, the woman shot the man in the chest. More details surrounding the shooting are still unknown.

The male officer was taken to Lutheran Hospital in critical condition where he later died. He was 44 years old.

Police have not said if the woman was taken into custody. Area 5 detectives and the Civilian Office of Police Accountability (COPA) are investigating.