Lopez and O'Neal had set a wedding date of October 27, according to the former couple's gift registry at Bed, Bath & Beyond. The officer, Samuel Jimenez, was 28 years old and had just completed his probationary period.
Chicago Police Superintendent Eddie Johnson said at a news conference that three people were killed in the shooting: Jimenez and two female staff employees of the hospital, one of whom police said was in a relationship with the shooter. A third person, who knew at least one of the two, subsequently attempted to intervene.
A large number of police cars and fire engines with flashing lights could be seen outside the hospital, according to video broadcast by the NBC 5 Chicago news channel.
O'Neal, an ER doctor at the hospital, was reporting for work when she was confronted by Lopez just before 3.30pm local time.
The van full of nursing home patients soon drove off and headed toward the exit just as police entered the parking lot. He ducked behind the bus for cover and watched as 50 to 100 people poured out of the hospital, including a victim on a stretcher.
Shootings across Chicago Monday left six people dead and two others wounded.
Mercy Hospital & Medical Center released a statement late Monday afternoon saying police officers have secured the facility and that patients are now safe. He's the second Chicago police officer killed in the line of duty this year. A police officer responding to the active shooter alert is among the victims. Another witness said he saw a gunman shoot someone multiple times in a parking lot.
Witness James Gray said Dr O'Neal fell to the ground and the shooter, "stood over her and shot her three more times".
Enzo Amore Removed from Ringside Area During WWE Survivor Series (Photo & Video)
It would've been great to see The Phenom at Survivor Series tonight, as he has a strong history with the event. The live streaming of WWE Survivor Series will be available on Sony Liv app and WWE app.
Thanksgiving week got off to a violent start Monday with four fatal shootings across the U.S. in a matter of hours.
The gunman, after killing the doctor, fired at arriving police officers with a single handgun, Johnson said.
After Lopez shot O'Neal again, he shot at a police auto that began driving towards him and then entered the hospital.
Officers locked down the hospital's first floor and closed off stairwells, eventually locating the shooter, who had sustained a fatal head wound.
The witness added that he heard roughly six gunshots and that one person in the crowd fired on returned gunfire at the assailant's auto as it drove away.
After shooting O'Neal, Lopez then killed a resident pharmacist, Dayna Less, and officer Samuel Jimenez during a shootout with police inside the hospital. It's not clear whether he was killed by police or someone else, or whether he died by suicide.
Dayna Less, a pharmacist, had recently graduated from Purdue University and was in her first year of residency at Mercy Hospital. Police were asking people to avoid the area.