A weapon was recovered from the parking lot of the hospital and it had been fired, Guglielmi said. Investigators determined the wounded person had been involved in the confrontation, police said.



A law enforcement source said the altercation may have involved mistaken identity.



A man who works in a store nearby said he saw someone in a hooded sweatshirt fire five shots into a maroon SUV before running into the parking lot of a nearby McDonald's.



A woman who lives on the second floor of an apartment building next to the McDonald's said she heard gunshots and, through her blinds, saw a man leaning over an SUV and firing at another car.



More than a dozen police and detectives converged on the scene, a commercial strip that includes the McDonald's, a Subway sandwich shop, a Starbucks and some apartments.



A McDonald's supervisor came to the scene to hand surveillance video over to police. Detectives were collecting other video and interviewing apartment residents who live nearby.



The sergeant, who works in the 19th District, will be placed on administrative duty for 30 days, per department policy.



Check back for updates.



Chicago Tribune's Megan Crepeau contributed.