FOLLOWING is the timeline of the shooting rampage on Tuesday at Robb Elementary School in Uvalde, Texas. Authorities said Salvador Ramos, 18, shot and killed 19 children plus two teachers after shooting his grandmother at the house they shared.

The information comes from statements by law enforcement and other public officials.

May 17 - Ramos legally buys a semiautomatic rifle on his 18th birthday at a sporting goods store in Uvalde.

May 18 - Ramos buys 375 rounds of ammunition from an unknown vendor.

May 19 - Ramos buys a second rifle at the same sporting goods store.

May 24, some time between, 11 and 11:15 a.m. CDT - Ramos sends a series of three private social media messages.

-- I'm going to shoot my grandmother.

-- I shot my grandmother. (His grandmother survives the attack with a gunshot wound to the face.)

-- I'm going to shoot an elementary school.

11:28 a.m. - Ramos wrecks his truck near the school after fleeing from the house where he shot his grandmother. He jumps out of the passenger side with a rifle and a bag. He sees two witnesses at a funeral home across the street and fires at them. He walks toward Robb Elementary School, climbs a fence into the parking lot and starts shooting at the school.

11:40 a.m. - The shooter walks into the west side of the school, apparently through an unlocked door, and fires multiple rounds.

11:44 a.m. - Officers from multiple law enforcement agencies begin to converge on the school. The gunman shoots at the first officers responding to the scene. The officers move back and take cover, then approach the suspect again.

Around this time, the shooter enters a classroom and massacres the students and teachers inside. Officers report hearing at least 25 gunshots from the classroom soon after arriving at the scene.

From 11:40 a.m. to about 12:40 p.m. - Officers on the scene call for more help, requesting tactical teams, specialty equipment, body armor, precision snipers and hostage negotiators.

About 12:40 p.m. - U.S. Border Patrol tactical teams arrive, enter the classroom, and kill the suspect.