Updated at 2:30 p.m. ET Tuesday

Chicago is mourning an ER doctor, a pharmacy resident and a police officer who were killed Monday after a man opened fire at Mercy Hospital & Medical Center on Chicago's South Side.

"This tears at the soul of our city. It is the face and a consequence of evil," Mayor Rahm Emanuel told reporters.

Chicago Police Superintendent Eddie Johnson identified the fallen officer as 28-year-old Samuel Jimenez, who joined the force last year and had been assigned to the city's 2nd District. He was a father of three, as Miles Bryan of WBEZ reported.

The police released video of dozens of police and emergency vehicles escorting Jimenez's body to the morgue on Monday evening.

Mercy Hospital has identified the victims as 38-year-old emergency room doctor Tamara O'Neal and 25-year-old pharmacy resident Dayna Less.

A Mercy Hospital representative, voice breaking with emotion, described O'Neal as a devoted Christian who was "dedicated to caring for her community, a wonderful individual." He said Less had recently joined the hospital after graduating from Purdue University.

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"A hospital should be a safe place," the representative said at a news conference. "It is especially senseless when a shooting occurs in the healing space of a hospital."

The gunman was killed during an exchange of fire with officers, though police say it's not clear whether the fatal shot was self-inflicted.

Chicago police identified the shooter as 32-year-old Juan Lopez, according to The Associated Press. At a Monday evening news conference, Johnson described what happened during the shooting.

Shortly before 3:30 p.m. local time, Johnson said, there was a verbal altercation in the hospital parking lot between "people who knew each other" — the gunman and a woman later identified as O'Neal.

The police superintendent said that a third person, who was described as a friend of one them, tried to intervene. That's when the gunman "lifted up his shirt and displayed a handgun," Johnson said. The friend fled into the hospital.

Johnson added that "911 received a call shortly thereafter that there was an assault taking place in the parking lot. A few seconds later, a second call came out of shots fired in the parking lot."

Police learned later that the gunman shot and killed O'Neal. Johnson said that when police arrived at the scene, the man "fired multiple shots at the officers before they could exit their squad car." The shooter then fled into the hospital, with police rushing in behind him.

"They engaged the offender for several minutes in the hospital, gunshots being fired by the offender and by the police," Johnson said. "During the exchange of gunfire in the hospital, one other female staff member was struck by gunfire fatally."

That woman was later identified as Less. "That poor woman got off the elevator, had nothing to do with nothing, and he shot her. Why?" Johnson added. Jimenez was fatally wounded in the exchange of fire inside the hospital, and Johnson credits him and other responding officers with saving "a lot of lives."

As Bryan of WBEZ reported, Clarence Smith was working in the emergency room when shots were heard, and he started helping patients move to safety.

"It was a scary situation bringing them out because CPD was doing their job and you don't know if the active shooter was down the hall or not," Smith said, "But you have to put the blinders on and keep moving forward. And that's what I did."

The hospital, which says it has been serving Chicago for more than 160 years, had completed an active shooter drill just last month.

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