CHICAGO (WGN) — A Chicago police officer was killed in a shooting Saturday on the city’s Southwest Side, and a second officer was critically wounded.

Three people are in custody.

Police identified the slain officer as 29-year-old Ella French. She had been on the force since 2018.

Police said officers were conducting a traffic stop 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 two officers who were shot were taken to the hospital, where French, who was shot in the face, died from her injuries.  

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 and the fifth female CPD officer to be killed while on duty.

Chicago police said the wounded officer, who has not been named, was shot three times and is currently in critical condition at the University of Chicago.

“I’m asking Chicago to wrap their arms around our police officers today and encourage them to continue their great work in protecting us all,” Chicago Police Superintendent David Brown said Sunday during a news conference.

Mayor Lori Lightfoot declared Sunday a “day of mourning” in Chicago, with flags flown 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 shot and was initially transported to Christ Hospital in stable condition.

Brown, citing preliminary information, said it is believed a male passenger fired the shots at police. The reason for the traffic stop was not immediately disclosed.

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.

French’s brother, Andrew, said he never questioned his sister wanting to be a police officer, just like she never questioned him when he said he was joining the Army.

“We wanted to do good for the world. My mom adopted both of us. She raised us to be of service, to care, to have integrity,” Andrew French said.

“My sister is a bada–. She always wanted to make a difference wherever, however, it was possible. I was never surprised when she said she was going to be a sheriff and then a cop. It just made sense,” he said.

Andrew French, who lives in Colorado, said both he and his sister were raised on the Southside, where their mother still resides.

Brown said so far this year, 38 officers have been shot at, and 11 have been hit 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 as line-of-duty deaths.

The Associated Press contributed to this report.