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A plainclothes Aurora police officer fired the first shot in Wednesday’s exchange between officers and a 21-year-old gunman who had been inside a car they were watching on the city’s near East Side, the police department announced Thursday.

While police initially reported officers only shot back after they were fired upon, they have since learned more about what happened, according to a statement.

“As the investigation into the officer-involved shooting from yesterday progresses, some new details have emerged,” police said in a statement Thursday on Facebook.

Four of the five people arrested Wednesday in connection with the shootout remain in police custody, while the only juvenile, a 15-year-old boy, was released without charges, police said Thursday afternoon.

However, police said, he may be charged later, depending on the investigation.

On Wednesday morning, several community policing officers were conducting an undercover operation in plainclothes, but wearing body armor that identified them as police officers, according to the statement.

The officers, in three separate unmarked vehicles, were watching a gray 1996 Mitsubishi Lancer as part of the operation targeting home burglaries and related gang activity on the 900 block of Grove Street, police said.

At about 10:50 a.m., a man got out of the Lancer and raised a handgun at two officers sitting in one of the unmarked cars, police said.

“Fearing for his life, the officer fired several rounds at the suspect,” police said in the statement.

The man, a 21-year-old Aurora resident, allegedly returned fire, then two officers in another unmarked vehicle also fired in the man’s direction, police said.

As the gunfire exchange continued, the officers took up “safer tactical positions” and a 1993 Toyota Corolla with two men inside drove up to the scene, police said.

The gunman ran to the Corolla and got in the back seat, joining the 21-year-old driver and 20-year-old front-seat passenger, police said.

During the shooting, a bullet struck the front seat passenger in the leg, police said.

In an apparent attempt to get away, the Corolla driver backed the car into a telephone pole at a high speed, police said.

Police said they took all three men inside the Corolla into custody without further incident.

The Mitsubishi, driven by a 15-year-old boy, also started to drive away, but was stopped and taken into custody about a block away, on the 900 block of Superior Street, while two passengers ran away, police said.

Police said they apprehended one of them, a 20-year-old man, nearby, and “believe they may know the identity” of the man who escaped.

Police recovered a gun from the Corolla, they said.

The man shot in the leg, the alleged gunman and the man who ran from the Mitsubishi were treated and released from area hospitals for injuries that were not life-threatening, police said. The alleged gunman sustained injuries consistent with the Corolla crash, and the man who fled had cuts, scrapes and a graze wound, according to the statement. Police said they didn’t know if the graze wound was from police gunfire or one of the suspects.

Those three men, along with the Corolla driver, remained in the Aurora jail Thursday afternoon as police continued their investigation. Police have not yet announced or confirmed any charges.

No officers were hit in the shooting and no other injuries were reported, police said.

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Twitter @hannahmleone

[email protected]

Twitter @hannahmleone