A gunman shot a doctor to death outside a Chicago hospital on Monday before storming the facility and killing a pharmaceutical assistant and a police officer during an exchange of gunfire and dying in the rampage, officials said.

The shooter knew the doctor he shot outside Mercy Hospital, Chicago Police Superintendent Eddie Johnson told a news conference, describing the initial killing as an act of domestic violence.

The gunman was the ex-fiance of the doctor, Chicago media outlets reported, with one witness saying he demanded a ring back.