Good morning. Today is Saturday, May 28th. I am Alicia Menendez in for Ali Velshi. I am here in

Yuvaldi, Texas, where police are admitting to a stunning string of failures in their botched response

to a school shooting at Rob Elementary that left 19 children and two teachers dead. Now, harrowing

new details revealing just how horrific the mass shooting was. NBC News has learned

that federal agents who responded to the scene were ordered by local police to wait and not enter

the school. But half an hour later, they defied that order and went in that is according to two

senior federal law enforcement officials.

Authorities say students were trapped inside a classroom with the gunman and repeatedly called 911

as local officers waited in the hallway for nearly an hour to take action.

Following days of confusion and misinformation, we are getting the clearest

timeline yet. Take a look. Around 1130 a.m., the shooter crashed his car, a 911 call was placed,

and shooting began outside the school. Within minutes, the shooter entered the school and fired off

100 rounds.

By 12.03 p.m., nearly 20 officers stood in a hallway outside of the classrooms, but it wasn't until 1250 that the classroom was breached using keys from a janitor.

By 1258, the shooter was killed. Some of the children who survived this massacre are describing what they saw while desperately waiting for help to arrive.

We were watching a movie and then we just heard banging.

My teacher got up to see what it was and then she yelled on Jake.

He has a gun.

Whenever he started shooting, we hit behind my teacher's desk.

The cops said, help if you need help.

And then they got one of the persons in my class said, help.

The guy overheard, and he came in and shot her. And then the cops barged into that classroom.

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