(CNN) -- Just one day before Dr. Tamara O'Neal and two others at Chicago's Mercy Hospital were shot and killed by her ex-fiancé, the former couple and her family were in church together, her father told CNN.
Juan Lopez, 32, shot O'Neal dead in the hospital's parking lot Monday afternoon before killing a Chicago police officer and a pharmacy resident inside the facility, authorities said.
Lopez, who police say also died of a gunshot, was O'Neal's fiancé until late September, when she called off the engagement, her father, Tom O'Neal, told CNN on Tuesday in a phone interview.
Tammy, as her relatives knew her, attended church services Sunday with Lopez and her family in Indiana, where she was from, Tom O'Neal said.
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 their 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."
How the shooting unfolded
Tamara O'Neal had just finished her emergency room shift at Mercy Hospital when Lopez approached her in the parking lot, argued with her and shot her, officials said. Police haven't said what led to the confrontation.
Responding police officers pursued the gunman into the hospital, exchanging gunfire with him for several minutes.
Lopez then shot and killed two more people -- Chicago police Officer Samuel Jimenez and 25-year-old pharmacy resident Dayna Less, who was exiting an elevator -- before Lopez also died, Chicago police Superintendent Eddie T. Johnson said.
Lopez also was killed; it is unclear whether Lopez died from police gunfire or a self-inflicted gunshot, Johnson said.
The hospital's emergency department, and several other parts of the hospital, still were closed Tuesday as a result of the shooting, spokesman Jim Ritter said.
The shooting drew large numbers of law enforcement and emergency responders. Vehicles with flashing lights cordoned off the blocks around the medical center.
When the gunman entered the facility, hospital worker Patricia Rinella and others barricaded themselves in a room, blocking a door with a copy machine, she told CNN affiliate WBBM.
"It was too close for comfort," Rinella said. "It just seemed like he was all over the place."
'Just the best person ever'
O'Neal lived a hard-working life: She recently took on medicine as a second career; she helped needy children get school supplies; and she was dedicated to church, agreeing to work much of the weekend to guarantee Sundays off, her boss recalled Monday night.
"Just the best person ever. Really," Dr. Patrick Connor, chairman of the hospital's emergency department, told reporters as he tearfully paid tribute to her.
A native of Portage, Indiana, O'Neal had graduated 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 "fundraised every year for disadvantaged children, for first, second, third grade, to get all their school supplies," he said.
And O'Neal was "completely dedicated to church" and its choir, arranging never to work on Sundays, Connor recalled.
"From last year, when I started here as chairman, that was her one thing that she wanted: 'I want to be able to go to church on Sundays,'" Connor recalled. "I said, 'OK, so you work Fridays and Saturdays, and we'll make sure you go to church on Sunday.'
"Just will be sorely missed."
Officer had just completed probation
Jimenez, the slain police officer, had just become a full-fledged member of the force, having completed probationary training period after joining the Chicago Police Department in February 2017, the police superintendent told reporters.
Jimenez and his partner went to the hospital when they heard dispatch traffic about the shooting there.
"They weren't assigned to that particular call, but they went," Johnson said, "because that's what we do."
Jimenez and Less, a pharmacy resident and recent Purdue University graduate, were killed during the shootout in the hospital, police said.
A bullet also hit the holster of a second officer, who was uninjured, 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.
Jimenez is survived by a wife and three children, Johnson said.