CHICAGO (CBS)—The Emergency Room doctor who was fatally shot by her ex-fiance in the parking lot of Mercy Hospital as she walked into work Monday afternoon had planned to marry the gunman last month, but she never walked down the aisle.

The circumstances of what to led Dr. Tamara O’Neal’s ex-fiance, Juan Lopez, to open fire in the parking lot and inside the hospital, leaving four dead, are still unclear. Lopez, who was shot by SWAT officers, is counted among the dead.

tamara oneal Emergency Room Doctor Tamara ONeal Was Fatally Shot By Ex Fiance, Juan Lopez

Dr. Tamara O’Neal was fatally shot by her ex-fiance as she was walking to work at Mercy Hospital.

Lopez and O’Neal had set a wedding date of Oct. 27, according to the former couple’s gift registry at Bed, Bath & Beyond.

The wedding date passed without the couple walking down the aisle, however.

The circumstances are unclear as to why the wedding was called off, or what drove Lopez to gun down his former fiancée as she walked into the hospital, wearing her medical scrubs.

CBS 2 learned that O’Neal studied at the University of Illinois at Chicago before working in Mercy Hospital’s emergency room.

O’Neal’s family and friends Monday night gathered at the hospital to remember the young doctor and say prayers.

Speaking at a press conference alongside Chicago Police Supt. Eddie Johnson, Mayor Rahm Emanuel asked others to consider the family’s plight.

“I ask each of us to hold our children, our loved ones all a bit closer,” Emanuel said. “Remember what is important in life and that there are others who are part of our larger family who will have a tear and a hole that will never heal–always a scar.”

O’Neal’s family is also praying for Chicago police officer Samuel Jimenez, who was killed in the shooting.

O’Neal was remembered by hospital staff speaking at a press conference Monday night as a church-going woman.