A gunman killed his ex-fiance, a specialist in emergency medicine, on Monday during a shooting at a Chicago hospital, BuzzFeed News reports.

Juan Lopez, 32, was accused in the shooting that also left a Chicago police officer and first-year pharmacy resident dead, Mayor Rahm Emanuel said during a news conference.

Dr. Tamara O’Neal, 38, was identified as Lopez’s former fiancee. The two were seen arguing outside Mercy Hospital, according to the BuzzFeed story.

Officer Samuel Jimenez and Dayna Less, 25, were the other two identified in the shooting.

Chicago Police Superintendent Eddie Johnson said Monday that O’Neal and Lopez were in “a domestic relationship,” adding that the shooting began in the hospital’s parking lot. Lopez allegedly shot O’Neal as she walked back into the hospital.

Police then chased the shooter into the hospital, where he began firing his gun. Less was struck and killed.

Jimenez, a married father of three, was struck and was taken to the University of Chicago Hospital, where he died, a Chicago Police Department spokesman told ABC 7. He had been a cop for only 18 months. “Today, the Fraternal Order of Police lost a valued brother, a courageous police officer who got up this morning, went to work and wanted to protect the city of Chicago,” said Kevin Graham, president of the Fraternal Order of Police.  “He did just that, but he did so with his life.”

O’Neal and Lopez were set to marry on Oct. 27, according to a registry on Bed Bath & Beyond’s website. She called off the wedding in September.

Lopez suffered a fatal gunshot wound, but it’s unclear whether it was self-inflicted or by a police officer, per ABC 7 Chicago.

Hospital staff said O’Neal was “the best person ever” and committed to being involved in her church and community.