What began as a milestone marking adulthood ended in tragedy after a suspected gunman used the AR-15 style rifle he purchased days after he turned 18, authorities said.
Uvalde High School student Salvador Ramos allegedly purchased two assault rifles just days after turning 18 and used them to carry out the second-worst school shooting in U.S. history -- all within a span of eight days, authorities said.
Ramos was known for fighting and threatening fellow students, some classmates told ABC News. He allegedly exhibited unusual behavior such as threatening classmates and claiming to have cut scars into his face, classmates said.
Authorities said during a press conference Wednesday afternoon that Ramos had dropped out of school.
Twenty-one people, including 19 third and fourth grade children, were killed in the attack, law enforcement officials said. Two teachers were killed, too. Another 17 people were wounded, including three law enforcement officers.
This is how the shooting unfolded:
Ramos moves in with his 66-year-old grandmother, Celia, Steve McCraw, director of the Texas Department of Public Safety, said during a press conference Wednesday afternoon.
Ramos meets "Cece," the recipient of several messages Ramos sent on the day of the shooting, on the social media app Yubo, she told ABC News.
The teen, who lives in Germany, said she and Ramos would "join each others live" streams on Yubo.
Cece alleged that there were other warning signs in hindsight, including that Ramos would ask others on Yubo "if they would want to be famous on the news."
Ramos turns 18, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives.
Ramos buys a semi-automatic rifle at a local sporting goods store called Oasis Outback, McCraw said.
Ramos purchases 375 rounds of ammunition for that rifle, McCraw said. It is not known where he purchased that ammunition.
Ramos buys a second semi-automatic rifle at the same store, McCraw said.
Morning: An Instagram account that law enforcement sources tell ABC News they believe is connected to Ramos sent another user on the social media platform a photo of a gun laying on a bed, according to a user who shared direct messages from the suspect's alleged account with ABC News.
11 a.m.: Ramos allegedly had three communications on the social media platform Meta which describes it as private one-to-one text messages. One message to an unknown recipient stated that he was going to shoot his grandmother, Texas Gov. Greg Abbott said in a press conference Tuesday.
Another one-on-one message said he had shot his grandmother, and the third said he was going to shoot an elementary school, but did not specify the school, Abbott said.
Ramos then shot his 66-year-old grandmother in the head at their residence, and she was able to run across the street and call police, McCraw said. She was taken to the hospital via helicopter and is still in critical condition, McCraw said.
11:28 a.m.:Ramos drove about 2 miles to Robb Elementary in his grandmother's truck crashing the vehicle outside the school, McCraw said. He exits the vehicle through the passenger side with a backpack full of ammunition and a rifle, authorities said.
11:30 a.m.: Police receive the first 911 call detailing the crash and shots fired.
11:32 a.m.: The gunman approached the west side of the campus. When he arrives at the school, he hops a fence and enters the parking lot, shooting “at the school” while still outside.
At one point, students heard banging on a window before their teacher saw the shooter with a "big gun," a fourth-grade student who was inside the school at the time said in an interview with ABC News, describing the "nonstop" gunshots that followed.
11:40 a.m.: Ramos walked into the west side of the school through an unlocked door, Texas Department of Public Safety regional director Victor Escalon said in a press conference Thursday.
11:43 a.m.: Robb Elementary School posts to Facebook that the campus has gone under lockdown "due to gunshots in the area."
11:44 a.m.: Local police and the district police officer make entry into the school and hear gunfire. They watch the suspect walk 20 feet into the school, make a right into another hallway and then walk 20 feet, Escalon said. He then turned left into a classroom with "doors open in the middle," Escalon said.
After the gunman went into a classroom that was connected internally to a second classroom and began shooting, "That's where the carnage began," McCraw said.
The initial responding officers did not initially enter the classroom due to the gunfire they were receiving and fell back, Escalon said. While they made calls to bring in backup, officers evacuated students and teachers.
12:17 p.m.: Uvalde Consolidated Independent School District announces the shooting on Twitter.
12:30 p.m.: Uvalde Fire Department scanner traffic calls on “additional firemen need to respond to Mill Street to establish a perimeter to assist Uvalde EMS and Uvalde PD."
Around 12:45 p.m.: Border patrol and tactical teams arrive and make entry before shooting and killing the suspect, Escalon said. Their focus then turned into a rescue operation, Escalon said.
1:06 p.m.: Police report that the suspected shooter was killed by officers at the scene after they broke into the classroom.
ABC News' Lucien Bruggeman, Matthew Fuhrman and Will Steakin contributed to this report.
Timeline: How the shooting at a Texas elementary school unfolded originally appeared on abcnews.go.com