Joan Motolilia spoke to ABC News and said that he got a call from his sister as the shooting was happening.
Motolilia said his sister, whose name he did not share, had an appointment at the Planned Parenthood.
"I heard the shots so I got really scared for my sister," he said. "As soon as I heard the shots, she hung up on me, and I didn't try to call her back, I didn't want to risk her life."
Motolilia said that he heard about three shots fired.
Three people, including a University of Colorado, Colorado Springs (UCCS) police officer, were killed in the shooting; nine other people were wounded. A suspect has been detained following a standoff, according to police.
Vicki Cowart, the president and CEO of the Rocky Mountain Planned Parenthood, released a statement saying "our concern is for the safety of our patients, staff and law enforcement."
An employee and a manager at a Supercuts near the the Planned Parenthood clinic also heard gun shots. They said they locked themselves in a salon's breakroom because they didn't know the location of the shooter.
"We were just sitting on our chairs looking out the window and we saw this red light like go by really fast and like going super fast, so we were like what heck is going on?" Caren Kesterson told ABC News.
"So we got up, and we looked outside and then like all of these cop cars showed up and they were behind their cars, yelling get down, get down. And I heard gunshots and everything. And then for awhile they were just shooting and I saw an officer go down," she said.
ABC News’ Kelley Robinson contributed to this report.