Video taken inside Inland Regional Center in San Bernardino Wednesday shows the tense minutes as people were evacuated from the building after at least two shooters entered the building and killed at least 14 people and injured 17.
Gabi Flores shared the video with NBC Los Angeles' media partner, KPCC.
It shows a group of people being directed by a law enforcement officer on how to leave the building.
The people, some whispering quietly to each other, are told to show their hands as they follow the officer down a hallway. A small child is seen walking between two women and holding their hands.
"Relax, everyone, relax," the officer is heard saying. "I take a bullet before you do, that's for damn sure. Just be cool, OK?"
The officer is later seen holding a long gun and standing by the door to the elevator.
Two suspects in the shooting, a man and a woman, are dead following a police chase and shootout, San Bernardino Police Chief Jarrod Burguan said Wednesday evening. Two of them were identified as Syed Rizwan Farook, 28, who worked for the San Bernardino County's health department, and Tashfeen Malik, 27. The pair were wearing "assault-style" clothing and armed with assault rifles and handguns, Burguan said.
Wednesday's shooting at the social services facility east of Los Angeles marked the deadliest mass shooting in the U.S. since the 2012 school shooting in Newtown, Connecticut, which left 20 children and six staff members dead.