(UVALDE, Texas) -- A Uvalde police officer had the opportunity to shoot the gunman before he entered the school, but did not take the shot for fear of hitting children, according to an official briefed on the investigation. The officer was armed with a AR-15-style rifle.
The officer who arrived with a rifle only had seconds to make the decision and feared he would hit children with his weapon, according to the official. The account was first reported by the New York Times.
The decision is the second missed opportunity for officers who were responding to reports of a gunman outside Robb Elementary School.
A Uvalde school district police force officer had arrived on the scene while the gunman was still outside, but drove past him, not seeing him in the parking lot.
Additional details on the investigation into the Uvalde school shooting are expected to be released next week. Two teachers and 19 students were killed after a gunman walked into the school through an unlocked door and opened fire.
Officials revealed it took 77 minutes from the moment the gunman entered the school to the moment he was shot and killed by Border Patrol officers.
Police response to the shooting is currently being investigated by the Texas Rangers, the U.S. Department of Justice and a special committee of the Texas legislature.
ABC News' Josh Margolin and Alyssa Pone contributed to this report.