WASHINGTON — The day after his 18th birthday, Salvador Ramos, a troubled teenager from small-town Texas, bought an assault rifle. A week later, he walked into a local elementary school, where he shot and killed 19 young children and two of their teachers.

Under fire over a police delay in confronting the shooter, authorities on Friday released the most complete timeline yet of how the attack unfolded:

11:28 am 

Ramos crashes a vehicle near Robb Elementary. He took the truck from the house where he lived with his grandmother, who he shot in the face before driving to the school.

He emerges from the wrecked truck with an assault rifle and fires on two bystanders at a nearby funeral home. He also repeatedly shoots at the school.

– 11:33 am –

Ramos enters the school through a door that was apparently unlocked. He goes into a classroom and unleashes a barrage of bullets, firing at least 100 rounds.

11:35 am 

Three Uvalde police officers enter the school. Two of them are wounded by bullets apparently fired by Ramos through a closed door.

The officers are later followed by three more from the same department, and a county deputy sheriff.

12:03 to 12:47 pm 

As many as 19 police officers are gathered in the hallway outside the classroom in which Ramos has barricaded himself.

At 12:03, police receive a 911 call from a child, giving her name and whispering that she is inside room 112 of the school.

After that she calls back multiple times.

At 12:10, she tells responders there are multiple dead. At 12:13 she calls again.

Again at 12:16, the student calls to say there are eight or nine students still alive.

At 12:21, three shots are heard over a 911 call made by another person.

At 12:36, the initial child calls back and is told to stay on the line. She tells 911 that the gunman has shot the door,

At approximately 12:43 and 12:47, she asks 911 to “please send the police now.”

12:15 pm 

The first members of a Border Patrol tactical team arrive on site.

12:50 pm 

The tactical team opens the classroom using keys obtained from a janitor, enters the room, and kills Ramos.

The child’s final call is cut off after she made it outside the classroom.