CHATHAM, Ill. (WLS) — The driver of a deadly after-school camp crash could have possibly suffered a medical emergency, according to Illinois State Police.

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The crash happened at the YNOT After School Camp, located at 301 Breckenridge Road, around 3:20 p.m. on Monday.

Four young girls and an 18-year-old were killed in the crash.

Other children were taken to area hospitals, ISP said some have already been released.

ISP initially said the driver, who was the only person inside the SUV, was taken to a local hospital for evaluation but was not injured.

The driver, a 44-year-old woman, is not in custody and has not faced any charges, ISP said.

On Thursday, ISP said investigators found a possibility that the driver could have experienced a medical emergency leading to the deadly crash.

ISP said the driver tested negative for alcohol and control substances.

The four victims were identified by the Sangamon County coroner as Ainsley Johnson, 8, of Chatham; Kathryn Corley, 7, of Chatham; Alma Buhnerkempe, 7, of Chatham and 18-year-old Rylee Britton of Springfield.

Governor JB Pritzker ordered flags at half-staff to honor the victims until the sunset of Saturday, May 3.

The driver formerly worked for the Illinois State Police, the agency investigating the crash. She worked at the ISP from June 2006 to August 2018, an ISP spokesman confirmed Tuesday.

Capitol News Illinois contributed to this report.