An off-duty Chicago police officer was critically shot early Wednesday morning. He has shown some response, giving a thumbs-up while undergoing treatment at the University of Chicago Medical Center, Superintendent Eddie Johnson said at an emotional news conference.

The shooting took place just after 1:30 a.m. in the 200 block of East 37th Street, a few blocks from Chicago police headquarters, where Johnson talked to reporters hours later, reports the Chicago Tribune.

Johnson said the 25-year-old officer, who is assigned to the Gresham District on the South Side, was parked on that block when he and his female passenger noticed a black four-door Toyota Corolla or Nissan Altima circling the block.

The officer pulled out into traffic to leave the area, but the suspicious vehicle pulled up behind him. Someone inside opened fire, blasting out the back window of the officer’s SUV and striking him in the back of the head, Johnson said. The woman was not injured.

Either the officer or the woman had just called 911 before gunfire erupted, according to the superintendent.

Officials did not identify the wounded officer by name.