Chicago police say a plainclothes officer died after being shot in the head while he was investigating reports of gunfire on the South Side.

Police Superintendent Jody Weis said Monday evening that several leads were being investigated but would not say if a suspect was in custody.

The slain officer was 27-year-old Alejandro "Alex" Valadez, who had worked in the department three years. Police say Valadez was shot twice early Monday from a person inside a vehicle.

Two other Chicago police officers have died on duty in the past year. Officer Nathaniel Taylor was shot in September while serving a search warrant. Officer Richard Francis was shot with his own weapon in July during a struggle with a woman on a city bus.