(UVALDE, Texas) -- 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 one of the worst school shootings 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:
Salvador Ramos asks his sister to purchase him a gun, according to Steve McCraw, director of the Texas Department of Public Safety. She refuses.
Feb. 28, 2022
In a four-person group chat on Instagram, Ramos discusses being a school shooter.
In a four-person group chat on Instagram, Ramos discusses buying a gun.
In a four-person group chat on Instagram, a user says to Ramos, "word on the street is you're buying a gun." Ramos replies, "Just bought something. RN."
Ramos posts on Instagram, "10 more days." A user replies, "are you going to shoot up a school or something?" Ramos responds, "No. And stop asking dumb questions. You'll see."
Ramos moves in with his 66-year-old grandmother, Celia, according to McCraw, from 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 lying 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 one-on-one direct communications on Facebook with Cece. The first message said 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.
It is not believed Cece saw the messages until after the shooting occurred.
Ramos shot his 66-year-old grandmother in the head at their residence. She was able to run across the street and call police, McCraw said. She was taken to the hospital via helicopter but is expected to survive.
11:27 a.m.: A teacher props open the school's west-facing exterior door, authorities said.
11:28 a.m.: Ramos drove about 2 miles to Robb Elementary in his grandmother's truck crashing the vehicle in a ditch outside the school, McCraw said. He exits the vehicle through the passenger side with a backpack full of ammunition and a rifle, authorities said. He opens fire on two people outside a funeral home across the street from the school. Neither person is injured.
11:30 a.m.: The teacher inside of Robb Elementary reemerges from the same door and calls 911 to report a man with a gun nearby.
11:30 a.m.: Police receive the first 911 call detailing the crash and shots fired.
11:30 a.m.: U.S. Marshals receive a call from a Uvalde Police Department officer requesting assistance in responding to a shooting at Robb Elementary School.
11:31 a.m.: Patrol vehicles arrive at the scene of the funeral home across the street.
11:31 a.m.: The suspect jumps one fence and approaches the school through a parking lot, firing multiple rounds at the school building. Contrary to previous reporting, he does not encounter any officers outside of the building.
11:31 a.m.: A Uvalde ISD officer who heard the 911 call about a man with a gun drove immediately to the area. Upon arrival, the officer sped toward who he thought was the gunman, but turned out to be a teacher not the suspect. In doing so, the officer drove past the suspect who was hiding behind parked cars, McCraw said.
11:32 a.m.: The gunman fires multiple rounds at the exterior of the school.
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.
11:33 a.m.: Ramos enters Robb Elementary through its west entrance -- the same one propped open by the teacher moments earlier, McCraw said Friday. After entering the building, Ramos walks approximately 20 to 30 feet before turning right down a corridor. After walking an additional 20 feet, Ramos enters a classroom door to his left.
He enters either classroom 111 or 112 and immediately fires more than 100 rounds at students and teachers. The two classrooms are connected internally.
11:35 a.m.: Three Uvalde Police Department officers enter the school using the same door as the shooter. They were later followed by three other Uvalde police officers and a county deputy sheriff, authorities said. A total of seven officers are in the school and two sustain "grazing wounds" from the gunman, who is firing down the hallway from behind a closed door, McCraw said Friday.
11:37-11:44 a.m: The shooter continues firing rounds at intervals, officials said.
11:43 a.m.: Robb Elementary School posts to Facebook that the campus has gone under lockdown "due to gunshots in the area."
11:51 a.m.: The police sergeant and additional officers arrive on scene.
12:03 p.m.: More officers continue to arrive in the hallway. There was as many as 19 officers at that time in the hallway, McCraw said.
12:03 p.m.: A 911 call is made from room 112 that lasts 23 seconds.
12:10 p.m.: The first group of deputy U.S. Marshals from Del Rio, nearly 70 miles away, arrives on site.
12:10 p.m.: The first 911 caller calls back and says there are multiple dead in the classroom, authorities said.
12:13 p.m.: The 911 caller calls again.
12:16 p.m.: The 911 caller calls again and says eight to nine students are still alive.
12:17 p.m.: Uvalde Consolidated Independent School District announces the shooting on Twitter.
12:19 p.m.: A call is made by someone else from room 111. The caller hangs up when another student told her to, McCraw said.
12:21 p.m.: The gunman fires again at the classroom door, forcing officers in the building to reposition themselves down the hallway away from the door.
12:21 p.m.: The caller in room 111 calls again and three shots are heard over the 911 call.
12:30 p.m.: Uvalde Fire Department scanner traffic says "additional firemen need to respond to Mill Street to establish a perimeter to assist Uvalde EMS and Uvalde PD."
12:36 p.m.: Another 911 call is made by the initial caller and it lasts for 21 seconds. The "student caller" was told to stay on the line and be very quiet. She tells 911 that the gunman shot the door, McCraw said.
12:43 p.m.: The 911 caller inside room 112 asks for police to be sent in.
12:46 p.m.: The 911 caller inside room 112 says she can hear police officers next door.
12:47 p.m.: The 911 caller inside room 112 again asks for police to be sent in.
12:50 p.m.: Officers from the Border Patrol tactical unit breach the classroom door using a set of keys acquired from a school janitor. Officers shoot and kill Ramos in the classroom. Officers then immediately engage in a "rescue operation," officials said Thursday.
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.