CHICAGO—A man killed three people and wounded four others in a series of shootings over roughly four hours that started on Chicago’s South Side and ended with his death in a shootout with police in a parking lot just north of the city. Investigators are trying to determine a motive for the attacks, which began Saturday afternoon with the killing of a 30-year-old University of Chicago student who was shot in the head while sitting in his car in a parking garage in the Hyde Park neighborhood, Chicago police Superintendent David Brown told reporters. He didn’t release any of the victims’ names. The shooter, 32-year-old Jason Nightengale, then “just randomly” walked into an apartment building a block away, where he shot a 46-year-old security guard who was sitting at the desk and a 77-year-old woman who was getting her mail, Brown said. The guard was pronounced dead at a hospital …