A potential sexual assault was stopped Tuesday after someone called police in Logan Square on the Northwest Side.
The witness saw a male on top of a woman about 10:40 p.m. on a sidewalk in the 2600 block of North Kedzie Avenue, Chicago police said.
The passerby called police, and the male walked away after he told the witness he knew the woman, police said.
The woman was not injured, but taken to Norwegian Memorial Hospital for observation, police said.
Area Five detectives are investigating.