(CNN) - Dr. Tamara O'Neal, Chicago Police Officer Samuel Jimenez and pharmacy resident Dayna Less were killed Monday by a gunman at a Chicago hospital.
The gunman, identified as Juan Lopez, also died in the incident. Lopez was shot in the abdomen and he shot himself in the head, according to the medical examiner's daily case ledger. It's not clear which caused his death.
Here is what we know about these three victims and the recollections of those they left behind.
Dr. Tamara O'Neal: Dedicated to helping others
Tamara O'Neal, known to relatives as Tammy, was an emergency room physician at Chicago's Mercy Hospital.
O'Neal, 38, was shot in the hospital's parking lot immediately after she finished her shift. Police said the gunman approached her in the lot, argued with her and then shot her.
The gunman had been O'Neal's fiancé until late September, when she called off the engagement, her father, Tom O'Neal, told CNN on Tuesday. Lopez "couldn't accept" that the relationship was over, her father said. The former pair had been scheduled to marry in October, he said.
O'Neal's father said she was a strong faith believer and that she and Lopez were not united in that faith.
"I just thank God for the 38 years we had with her. I was thinking we'd have a lot longer," Tom O'Neal said. "We were expecting being grandparents, spoiling the grandchildren."
"She's tremendously loved by her family. This isn't all a loss," he said. "The things she did, we're going to hold on to those things."
O'Neal took on medicine as a second career, she helped needy children get school supplies and was dedicated to church, agreeing to work much of the weekend to guarantee Sundays off, her boss recalled.
"Just the best person ever. Really," Dr. Patrick Connor, chairman of the hospital's emergency department, told reporters.
Often treating shooting victims, Connor said O'Neal was concerned about gun violence.
"She talked about it a lot," he said. "And about the incessant national tragedy that all these people are dying needlessly."
A native of Portage, Indiana, O'Neal graduated from the University of Illinois-Chicago's emergency medicine program in 2016, he said.
"Simply one of the most fascinating, hard-working persons," Connor said. "Medicine was a second career for her. ... She just started practicing here two years ago."
O'Neal was a niece of Southern Illinois University assistant men's basketball coach Anthony Beane Sr., her father said. She was a cousin of Beane's son, SIU basketball player Darius Beane, who learned about his relative's death from his father after a game Monday night, head coach Barry Hinson said.
"I would like for our fans to keep that family and other families' members in their prayers," Hinson told reporters.
Officer Samuel Jimenez: 'Heroic actions'
Samuel Jimenez, the slain police officer, had just become a full-fledged member of the force, having completed a probationary training period after joining the department in February 2017, police Superintendent Eddie Johnson told reporters.
Jimenez, 28, and his partner went to the hospital when they heard dispatch traffic about the shooting.
"They weren't assigned to that particular call, but they went," Johnson said, "because that's what we do."
Jimenez is survived by a wife and three children, Johnson said. The responding officers "saved a lot of lives because we just don't know how much damage he (the gunman) was prepared to do," Johnson said.
A procession was held Monday night, and Chicago police posted on Twitter to pay final respects.
"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," the department tweeted.
A wake is scheduled for Sunday and Jimenez' funeral is Monday morning, police said.
Dayna Less: She was tenacious
Dayna Less, 24, was a first-year pharmacy resident training to be a pharmacist, the hospital said. She recently graduated from Purdue University and joined the hospital staff in July.
She was fatally shot by the gunman as she was getting off the elevator, Johnson said. She had "nothing to do with" anything related to the gunman.
As a teenager, Less had a severe headache disorder that left her largely unable to go to school, her father, Brian Less, said at a press conference Tuesday. She eventually found a doctor at Georgetown University who performed two surgeries that addressed the symptoms, he said.
"I have a picture where she traded two black eyes for a smile," he said. "She came out of surgery, she was all beat up, but she had a smile for the first time in a year."
The experience made Dayna tenacious in her career and how she took care of herself, he said.
Brian Less told the story of when his daughter went to Kenya as a pharmacy student on rotations. When she got there, the doctors in Kenya went on strike, leaving the pharmacists and the few others with an education in charge of the patients.
Dayna felt overwhelmed, he said, but she still wrote on her blog about her "wins" of the day and focused on the positive things she encountered.
"She was a positive person," he said. "That's who she was."
Brian Less said he didn't want his daughter to be remembered as a victim.
"Dayna was a very special person. She had unique gifts," he said, according to CNN affiliate WLS. "She was intelligent, she was funny, she was kind, she was a good friend."
Violence a "serious public health issue"
Mercy hospital, a member of Trinity Health, released a statement mourning O'Neal and Less as well as commenting on the importance of addressing violence in all of its forms.
"Trinity Health colleagues, nurses, physicians and clinicians are committed to combatting violence -- in all of its forms -- everywhere. Violence in all of its forms is a serious public health issue. By standing up against all violence, including workplace violence, domestic violence, gun, street and gang violence, we can be agents of changes that make our communities healthier. "
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