A police officer, a doctor and a pharmaceutical assistant are dead after a Monday afternoon shooting at Chicago's Mercy hospital, Mayor Rahm Emanuel said.
The suspect, who was in a relationship with the one of the victims, also died, Chicago Police Superintendent Eddie T. Johnson said.
Chicago Police identified the deceased officer as Samuel Jimenez.
Police secured the hospital earlier Monday evening and the patients are safe.
Earlier, Chicago Police said an officer and an offender were shot. The incident drew large numbers of law enforcement and emergency responders. Vehicles with flashing lights cordoned off the blocks around the busy medical center.
Witness Steven White told CNN's Ryan Young that he was in the emergency room when he saw the shooter firing at police.
"We heard some shots so we all ran to the emergency window, we see this guy out there, military style, shooting at the police -- pow, pow, pow," he said.
When White looked outside he said he saw a person lying on the ground by the main entrance. The shooter turned around and opened fire again before running inside the main entrance.
"I don't even have words to say how I was feeling," White said. "It's sad, you can't even come to the hospital for treatment."
At least 15 medic units were sent to Mercy hospital, Chicago Fire Department Public Information Officer Larry Merritt said.
The FBI is assisting local authorities, a spokeswoman said.
Democratic Sen. Dick Durbin of Illinois thanked law enforcement members for their response.
"My heart is with Mercy Hospital in Chicago tonight. I am praying for the victims, their families, and those who were injured during the shooting this afternoon. And I am extremely grateful to the Chicago Police Department who responded with bravery," he said on Twitter.