UVALDE, Texas  — A Texas law enforcement official says the gunman who killed 19 children and two teachers at a South Texas elementary school was able to enter without any confrontation, through a door that was apparently unlocked.

Salvador Ramos, 18, crashed his pickup truck outside the school at 11:28 a.m. (1628 GMT) on Tuesday, fired several shots at two bystanders across the street and walked into an unlocked door of the school at 11:40 a.m. (1640 GMT), Victor Escalon, a spokesman for the Texas Department of Public Safety, told a news conference.

Escalon said officers arrived and entered the school four minutes later but took cover after Ramos fired multiple rounds at them. He barricaded himself in a fourth-grade classroom, where he shot his victims, mostly 9- and 10-year-olds, in the deadliest U.S. school shooting in nearly a decade.

An hour elapsed before a U.S. Border Patrol tactical team breached the classroom and killed Ramos, Escalon confirmed, a timeline that has prompted questions about whether law enforcement could have intervened sooner.

The newly detailed account came hours after videos emerged showing desperate parents outside Robb Elementary School during the attack, imploring officers maintaining a perimeter to storm the building, with some fathers having to be restrained.

Law enforcement authorities faced mounting questions and criticism Thursday over how much time elapsed before they stormed a Texas elementary school classroom and put a stop to the rampage by a gunman who killed 19 children and two teachers.

-Ap/Reuters