Around 2 p.m., police say a 36-year-old man was inside his Logan Square garage in the 2700 block of North Monticello when a 53-year-old man armed with a knife approached him.
The victim pulled out a gun and shot the offender in the head, police said.
The offender was pronounced dead at the scene. The victim did not sustain any injuries, police said.
Area Five detectives are investigating.