CHICAGO (CBS)– Dr. Basem Khishfe is the emergency room doctor who tried to save his friend and colleague, Dr. Tamara O’Neal, along with others, after she had been shot by her ex-fiance outside of Mercy Hospital on Monday.

He says he is still in shock and has not fully processed what happened.

“As emergency physicians, we’re very good at being detached,” he said.

Khishfe has worked at Cook County and Mt. Sinai hositals where he treated bullet wounds. While showing the spot where he tried to save a gunshot victim this week, he said it’s different when the patient is a colleague.

“When it’s someone you know, someone you’ve had dinner with, someone you’ve had drinks, someone you kind of shared a life with, it’s different,” the emergency room doctor said.

Khisfe was finishing up a shift in the ER when police responded to the incident Mercy Hospital.

“One of the other doctors was running and she literally grabbed me by my hand and was like, ‘active shooter’,” he said.

The shooter shot Dr. O’Neal in the parking before bursting into the hospital.

Khisfe got to the breakroom and heard a couple of shots. After waiting, he said the coast was clear and he was able to tell an officer that he is a doctor.

He ran to O’Neal with an officer and started doing CPR on her.

Khishfe sprinted back inside to help another co-worker who had been shot, pharmaceutical resident Dr. Dayna Less. He also treated Chicago Police Officer Samuel Jimenez with most of the ER staff still evacuated or in hiding.

“You’re already working in an overwhelming situation and you’re undermanned in this situation so it makes it 20,000 times harder,” Khishfe said.

Khishfe said administrators told him to take the week off.

“Today, I insisted on coming, I wanted to come even though I wasn’t scheduled just to be able, because it’s my family,” he said.

Khishfe said he mustered up the strength Wednesday to show O’Neal’s family around the emergency room where she worked alongside him for a year and a half.

Khishfe says he’s feeling guilty for liking the shooter when he first met him as O’Neal’s fiancée, at a Christmas party last year.

Khisfe says he never imagined the shy man would turn into a killer.