These are the 3 victims in Chicago’s Mercy Hospital shooting

CHICAGO — Chicago police say a domestic dispute led to a shooting that left three people and the gunman dead at Mercy Hospital on Chicago's South Side, according to WGN.

Police responded to the scene at Mercy Hospital and Medical Center at 2525 S. Michigan Ave. for reports of shots fired just before 3:30 p.m. Monday.

A Chicago police officer, an emergency room doctor and a first-year pharmacy resident, were all killed in the attack.

The gunman, Juan Lopez, 32, also died, but it is unclear whether he died from police gunfire or a self-inflicted gunshot wound.

The shooting was a domestic incident, and the gunman's first victim was an ER doctor with whom he had previously had a relationship with.

These are the victims:

Chicago Police Officer Samuel Jimenez

Chicago Police Officer Samuel Jimenez, 28.

The Chicago Police Department have identified the slain officer as 28-year-old Samuel Jimenez. He joined the department in Feb. 2017 and just recently completed his probationary period to officially become a full-fledged officer. Jimenez was married and the father of three children.

Jimenez was killed during a shootout with Lopez. Police spokesman Anthony Guglielmi says Jimenez didn't typically work in the hospital area, but that the officer responded when he heard that shots were fired. He says it "speaks volumes about his character."

The CPD tweeted the following statement early Tuesday morning:

"Today, we mourn Chicago Police Officer Samuel Jimenez. His heroic actions saved countless lives. He ran toward danger. He ran toward those shots. He ran into fire. Selflessly. Samuel Jimenez: altruism personified."

Jimenez is the second officer to be killed in the line of duty this year.

Dr. Tamara O'Neal

Dr. Tamara O'Neal

Tamara O'Neal, 38, an emergency room physician, was known as very charitable and deeply religious. She never worked Sundays because of her religious faith. O'Neal had broken off her engagement to the gunman, Juan Lopez, back in September.

Lopez and O'Neal had been arguing in the hospital parking lot before he displayed a handgun and fatally shot her.

Dr. John Purakal, a colleague of O'Neal, said in an emotional tweet: "I knew her, trained with her, saved lives with her and tonight, tried to save her life. Tonight, I broke down in front of my coworkers when we lost her, and tonight I held hands with her mother in prayer. Tonight, we lost a beautiful, resilient, passionate doc. Keep singing, TO."

Dr. Dayna Less

Dr. Dayna Less, 25

Dayna Less, 25, a first year pharmacy resident, had recently graduated from Purdue University and started working at Mercy Hospital in July. Less was planning a wedding next year in Indiana. She also had plans to go home this week for Thanksgiving.

Her family said she should not be remembered as a victim, but as a beautiful daughter who overcame adversity and dared to succeed in a tragic world.

Brian Less, Dayna's father, released the following statement:

"Dayna suffered a headache disorder when she was 15.  Not migraines but worse.  And through a series of surgeries and almost 2 years of recovery was able to regain her life. She realized then that she could not sit still and only wanted to help others and the less fortunate. She graduated Lake Central High School and went to the Purdue Pharmacy program where she graduated this past May after 6 years. She spent time in Kenya helping at a hospital. She started a blog, www.mydaughtersheadache.com, and helped hundreds of children with a similar affliction find hope and help. She loved helping others. She was good at her job because it helped others. She was forged in her own adversity which made her the strongest person I will ever know. After dating Adam for almost 10 years, her high-school sweetheart, they were to be married on June 1st of 2019. We thank everyone for their prayers. We pray for the other families touched by this tragedy and the many, many others in recent months. May her memory be eternal and that we can finally learn how to stop these senseless acts."

Less was killed as she was getting off a hospital elevator.