UVALDE, Texas (AP) — It was 11:28 a.m. when the Ford pickup slammed into a ditch behind the low-slung Texas school and the driver jumped out carrying an AR-15-style rifle.

Twelve minutes after that, authorities say, 18-year-old Salvador Ramos was in the hallways of Robb Elementary School. Soon he entered a fourth-grade classroom. And there, he killed 19 schoolchildren and two teachers in a still-unexplained spasm of violence.

At 12:58 p.m., law enforcement radio chatter said Ramos had been killed and the siege was over.

What happened in those 90 minutes, in a working-class neighborhood near th...