Updated 11 p.m.

A gunman opened fire Monday at Mercy Hospital on the city’s South Side, killing three people, including a police officer, before the suspect also died, authorities said.

Chicago Police Superintendent Eddie Johnson confirmed the gunman killed a doctor at the hospital with whom he’d had a relationship, a Chicago police officer, and a hospital staff member around 3 p.m. It was not immediately clear if the gunman took his own life or was killed by police.

“The city of Chicago lost a doctor, pharmaceutical assistant, and a police officer, all going about their day, all doing what they loved,” Mayor Rahm Emanuel said. “This just tears at the soul of our city. It is the face and a consequence of evil.”

Johnson said a “verbal altercation” occurred in the hospital parking lot between a man and 38-year-old Dr. Tamera O’Neal, who worked at Mercy as an emergency room physician. The two had been in a relationship, and a “broken engagement” possibly sparked the argument, sources told the Chicago Tribune. A friend attempted to intervene in the dispute and fled into the hospital for help after the gunman lifted up his shirt to reveal a gun. The gunman then fatally shot O’Neal in the parking lot, witnesses said.

One witness, James Gray, said the gunman shot O’Neal in her in the chest and then “stood over her and shot her three more times.”

Officers arrived and chased after the gunman as he ran into the hospital, Johnson said. Gunshots were exchanged for several minutes — during which the gunman fatally shot a pharmaceutical assistant, 25-year-old Dayna Less, who was stepping off an elevator and Officer Samuel Jimenez, of the 2nd District, who was responding to the call.

Jimenez, a 28-year-old father of three, joined the department in February 2017. Mayor Emanuel noted the shooting happened just hours after the Chicago Police Department held one of its largest graduation ceremonies early Monday.

The procession for Ofc. Jimenez has begun. CPD and our federal and state partners pay our final respects to a hero. pic.twitter.com/f28V2x8l9G

— Chicago Police (@Chicago_Police) November 20, 2018

The Associated Press contributed to this report.

This story is developing. Check back for updates.