The driver of a car that barreled through a building used for a popular after-school camp in central Illinois, killing three children and a teenager, was not under the influence of drugs or alcohol and may have had a medical emergency, police said Thursday.

No decisions have been made on whether to file charges against the 44-year-old driver, Illinois State Police Director Brendan F. Kelly said at a news conference. The driver is not in custody, Kelly said.

Evidence that she may have had a medical emergency was "not conclusive" and the investigation is ongoing, Kelly said.

The car went off the road Monday, crossing a field and smashing into the side of the building in Chatham used by Youth Needing Other Things Outdoors, also known as YNOT. It traveled through the building, striking people before exiting the other side.

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Six other children were hospitalized. Four of them remained hospitalized, including one in critical condition, a state police spokesperson said after Thursday's news conference.

Those killed were Rylee Britton, 18, of Springfield, Ainsley Johnson, 8, Kathryn Corley, 7, and Alma Buhnerkempe, 7. All of the children were from Chatham, a community of about 15,000 outside the Illinois capital of Springfield.

The driver was not injured but was taken to a hospital for evaluation after the crash, Kelly said. She voluntarily submitted blood and urine samples that tested negative for drugs and alcohol, he said.

"Some evidence has been developed indicating the possibility of a medical emergency leading up to the crash," Kell said. "However, the investigation of this information and other evidence has not yet concluded and will continue until all leads and research have been exhausted."

He would not elaborate on the possible health issue or say what evidence investigators have indicating a medical emergency may have occurred. He also would not say whether the driver was conscious and alert when emergency responders reached her.

Security camera footage showed the vehicle was "a substantial distance" away when it left the roadway, said Jamie Loftus, founder of YNOT Outdoors. It crossed the field, a road, the sidewalk and YNOT's parking lot before crashing through the building "with no apparent attempt to alter its direction," Loftus said earlier this week. The vehicle then crossed a gravel road and crashed into a pole and fence.

Kelly said the vehicle traveled more than 1,300 feet (396 meters) but would not elaborate and also would not say how fast the vehicle was moving.

He said he could not provide a timeline for completing the investigation and said charges, if appropriate, would be up to the Sangamon County state's attorney.

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Associated Press writers Scott Bauer in Madison, Wisconsin, and Sophia Tareen in Chicago contributed.