CHICAGO • Police were seeking a motive for a shooting rampage outside and inside a Chicago hospital that left four people dead, including the gunman, a physician who was his former girlfriend and a police officer, officials said.

The gunman, Juan Lopez, 32, was the former boyfriend of Dr Tamara O'Neal, 38, who was shot and killed outside Mercy Hospital on Monday, Chicago Police Department officer Jose Jara said.

Chicago police superintendent Eddie Johnson on Monday described that first killing as an act of domestic violence.

"There's no doubt in my mind that all of those officers who responded were heroes and they saved a lot of lives because we just don't know how much damage he (the gunman) was prepared to do," Mr Johnson said.

Another report quoting the police said shots were first fired in the parking lot when Lopez got into an argument with Dr O'Neal.

The Chicago Tribune, which said Dr O'Neal was his former fiancee in one article, reported that she had ended their engagement and that Lopez went to the hospital to demand his ring back.

Officials and witnesses described how the argument escalated when a friend tried to intervene. Lopez brandished a gun, causing the friend to flee, and shot Dr O'Neal repeatedly.

After killing Dr O'Neal, Lopez fired at arriving police officers with a handgun, then entered the hospital and exchanged gunfire for several minutes with officers who followed him, Mr Johnson said.

Lopez also died but it was not immediately clear if he shot himself or was struck by a police officer's bullet.

Officer Samuel Jimenez, who joined the Chicago police last year, died during the gunfight, officials said. Mr Jimenez, 28, was married with children and was the second city officer killed on duty this year.

Dr O'Neal had worked as a resident and emergency room physician at Mercy Hospital for about two years and was heavily involved in her church, the Chicago Tribune reported.

The paper cited hospital employees as saying Dr O'Neal was Lopez's former girlfriend. One witness said Lopez was harassing Dr O'Neal before the attack.

"I knew her, trained with her, saved lives with her and tonight, tried to save her life," Dr John Purakal of the University of Chicago Medicine, wrote on Twitter. "Tonight, I broke down in front of my co-workers when we lost her, and tonight I held hands with her mother in prayer. Tonight, we lost a beautiful, resilient, passionate doc."

Doctors and patients fled the hospital during the attack.

Pharmacy assistant Dayna Less, 24, was shot and killed as she left an elevator, Mr Johnson said.

Another officer was spared injury when a bullet lodged itself in his gun holster.

In Denver, another shooting left one person dead and four wounded on Monday.

At least one suspect remained at large after the shooting at a downtown street corner.

Police said the injuries were believed to be non-life-threatening.

REUTERS, WASHINGTON POST