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CHICAGO (WGN) — A Chicago police officer was killed in a shooting Saturday on the city’s southwest side. A second officer was injured and remains in the hospital in critical condition.

Three people are in custody.

Police identified the slain officer as 29-year-old Ella French.

Police said officers were conducting a traffic stop in the 6300 block of South Bell Avenue in the West Englewood neighborhood just around 9 p.m.

Officers had stopped a vehicle with three occupants inside, two men and one woman. According to police, the occupants inside the vehicle opened fire towards the officers, leading to an exchange of gunfire.

The officers were struck by gunfire at the scene. Both were taken to the hospital where one of the officers, French, died from her injuries.  

On Sunday, Chicago Police Superintendent David Brown, Mayor Lori Lightfoot and other police officials held a news conference.

French was assigned to the police department’s community safety team working with the gun task force. She is the first line of duty death for the department in nearly three years. She is the fifth female CPD officer to be killed while on-duty.

The name of the second officer critically injured has not been released.

Lightfoot declared Sunday a “day of mourning” in Chicago and flags would be at half staff.

“Tragedy has struck, again. We mourn the loss of a young officer, and as I did privately in the early morning hours, I want to publicly offer condolences to her mother, her brother, family and friends,” she said. “Please keep this officer in your prayers. Also keep the other officer who was shot in your prayers and his family and his friends and every day for the rest of his life, uplift him and support him. They will need our help as a city. Two young people, doing what we ask, service over self, commitment, and dedication.”

One of the two men taken into custody was struck by gunfire and was initially transported to Christ Hospital in stable condition.

Brown, citing preliminary information, said it is believed a male passenger was the person who fired shots at police.

Brown said much of the incident was caught on body camera and the Civilian Office of Police Accountability will determine the release of the footage. The investigation is ongoing.

Brown also said 38 officers have been shot or shot at so far this year. 11 of those officers have been struck by gunfire.

The last Chicago officer shot to death in the line of duty was 28-year-old Samuel Jimenez, who was killed after responding to a shooting at Mercy Hospital on Nov. 19, 2018.

Two officers, Conrad Gary and Eduardo Marmolejo, died when they were struck by a South Shore train while pursuing a suspect on Dec. 17, 2018. The department also considers the COVID-19 deaths of four officers last year line-of-duty deaths.

The Associated Press contributed to this report.