Springfield Police Chief Paul Williams said one of his officers is among four people who were killed by an active shooter late Sunday night at the Kum & Go on Chestnut Expressway near Highway 65.

Williams said two others, including another officer, were shot but still alive.

The shooter died from a self-inflicted gunshot, according to the police chief.

Williams said the deceased officer is Christopher Walsh, who had been with the department for 3 and a half years.

The other injured officer, Josiah Overton, suffered non-life-threatening injuries, the chief said.

Police identified the shooter as 31-year-old Joaquin S. Roman of Springfield.

Williams said Sunday night's incident started at 11:24 p.m. when a shots fired call was reported at Battlefield Road and Lone Pine Avenue.

As officers made their way to that scene, Williams said there were reports of other shootings as the suspect traveled northbound through the city's east side.

"In essence we had a roving active shooter moving from the south side of the city up," Williams said.

Eventually, Williams said the suspect crashed his vehicle outside of the Kum & Go on Chestnut Expressway and Prince Lane, walked inside and began shooting customers and employees.

Williams said Walsh and Overton were the first officers on scene at the Kum & Go, and they were immediately fired upon by the suspect who was inside the store as the officers approached in the parking lot.

The next arriving officers removed Walsh and Overton from the scene and then went inside the store where they found three dead civilians, one injured civilian and the suspect who had apparently died by suicide, according to Williams.

Williams said Officer Walsh was transported to the hospital where he died.

In a news release Monday afternoon, police identified the three civilian deceased victims as Troy Rapp, 57, Shannon Perkins, 46, and Matthew Hicks-Morris, 22. Rapp was a Kum & Go employee, Perkins was employed by WCA Waste Corporation and Hicks-Morris was a customer in the store.

Police say the fourth civilian victim was in the hospital Monday in critical condition.

The chief said early Monday morning he had no idea what the shooter's motivations might have been.

The incident elicited a huge response from the department. Dozens of patrol cars lined Chestnut Expressway during the early morning hours as the thoroughfare was blocked off in both directions.

Williams asked the public to stay away from that area throughout the day on Monday.

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As he fought back tears at a news conference early Monday morning, Williams commended officers Walsh and Overton for their bravery.

Springfield Mayor Ken McClure expressed his condolences to Officer Walsh's family.

"We ask the community for prayers for the families, as well as for wounded Officer Josiah Overton and another wounded person who was in the store at the time of the shooting," McClure said in a statement posted to the city's social media pages. "We are indebted and very grateful for our officers who exhibit extreme bravery for our protection. Officer Walsh made the ultimate sacrifice. Our community mourns his loss."

Chief Williams said Walsh was a U.S. Army veteran and was active in the Army Reserve.

Walsh, 32, is a Springfield native who graduated from Glendale High School. He is survived by a wife and daughter.

Police were seen Monday morning responding to the Abbey Apartments in south Springfield with a BearCat armored vehicle. Department spokeswoman Jasmine Bailey said that police action was related to the Kum & Go shooting but she declined to give specifics on what police were doing or if anyone involved in the shooting lived at those apartments.

Court records indicate Roman lived at the Abbey Apartments as recently as December.

The Abbey Apartments are about 2 miles away from the intersection of Battlefield Road and Lone Pine Avenue where Sunday's incident began.