Mercy Hospital Shooting: What We Know

(CBS) -- A shooting rampage at Mercy Hospital left four people dead Monday. Here is what we know:

• The victims include a Chicago Police Officer, Samuel Jimenez, 28; an emergency room doctor, Tamara O'Neal; Dayna Less, 24, a pharmacy resident; and the gunman, Juan Lopez. 
• Lopez first confronted O'Neal in the hospital parking lot and shot her multiple times. The two were once engaged to be married but the planned wedding never happened.
• After shooting O'Neal, Lopez shot at responding police officers and entered the hospital in the 2500 block of South Michigan. While inside, he fatally shot Jimenez and the pharmacy worker, who was in an elevator.
• Terrified patients and workers described hearing the gunshots and scrambling to safety as the hospital activated an active shooter alert. 
• Lopez was then killed, although it is unclear how he was shot, Chicago Police Supt. Eddie Johnson said.
• Johnson also said responding officers "saved a lot of lives.  We don't know how much damage he was prepared to do."