The man who drove an SUV into Woodfield Mall in suburban Schaumburg on Friday afternoon acted alone, police said.
There was no indication that the attack was pre-planned, and the incident didn't appear to be related to terrorism, Schaumburg police said at a news conference on Friday night.
Chaos erupted at around 2:30 p.m. when the unidentified 22-year-old man drove his vehicle inside of the popular suburban Chicago shopping center. Three people were taken to the hospital with non-life threatening injuries, police said.
Several bystanders, including two off-duty police officers, detained the suspect immediately following the incident.
The driver was arrested, but has not been identified. Formal charges had not been announced by the Cook County State's Attorney's Office as of Friday evening.
Police and fire officials remained on the scene at the mall throughout the evening.
"The authorities believe this to be an isolated incident involving one person who has been arrested," Woodfield Mall management said in a statement. "We are grateful no one was injured, and thank our security team and the police for their quick response."