Timeline: How the shooting at a Texas elementary school unfolded

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.

Twenty-one people, including 19 third and fourth grade children, were killed in the attack, law enforcement officials said. Two teachers were among those killed. Another 17 people were wounded, including three law enforcement officers.

This is how the shooting unfolded:

September 2021

Salvador Ramos asks his sister to purchase him a gun, according to Steve McCraw, director of the Texas Department of Public Safety. She flatly refuses.

Feb. 28, 2022

In a four-person group chat on Instagram, Ramos discusses being a school shooter, according to McCraw.

March 1

In a four-person group chat on Instagram, Ramos discusses buying a gun, according to McCraw.

March 3

In a four-person group chat on Instagram, according to McCraw, a user says to Ramos, "word on the street is you're buying a gun." Ramos replies, "Just bought something. RN."

March 14

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."

March 20

Ramos moves in with his 66-year-old grandmother, Celia, according to McCraw, from a press conference Wednesday afternoon.

Around May 9

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 other's 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."

May 16

Ramos turns 18, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives and multiple law enforcement sources.

May 17

Ramos buys a semi-automatic rifle at a local sporting goods store called Oasis Outback, McCraw said.

May 18

Ramos purchases 375 rounds of ammunition for that rifle, McCraw said. It is not known where he purchased that ammunition.

Friday, May 20

Ramos buys a second semi-automatic rifle at the same store, McCraw said.

Tuesday, May 24

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.

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.

Shortly after 11 a.m.: Ramos shot his 66-year-old grandmother in the head at their residence, according to McCraw. He flees. She was able to run across the street and call police, McCraw said. She was taken to the hospital via helicopter. She has survived.

11:27 a.m.: A Robb Elementary School teacher exits the school's west-facing entrance door to transport food from her parked car to the classroom, The Associated Press reported and the Texas Department of Public Safety confirmed to ABC News on Tuesday. The teacher witnesses the car wreck and runs inside to retrieve her phone, using a rock to keep the door propped open.

11:28 a.m.: Ramos crashes his vehicle into a ravine adjacent to Robb Elementary School, according to McCraw. He emerges from the passenger side of the vehicle wielding a Daniel Defense AR-15-style assault rifle. Ramos wore a backpack containing ammunition and tactical gear, including a vest that could hold ammunition, sources said, but there was no armor or fabric that would protect him from gunfire.

After exiting the vehicle, Ramos fires four shots at two witnesses outside a nearby funeral home, neither of whom was struck, and then makes his way toward the school, surveillance video released earlier this month shows.

11:29 a.m.: The Robb Elementary teacher calls 911 to report the car crash. While on the phone with police, she returns to the propped-open door and sees Ramos approaching the school with a gun, which she tells the dispatcher. The teacher then removes the rock she had used to prop open the door and shuts the door -- but the door does not lock, the AP reported and Texas DPS confirmed to ABC News.

McCraw said initially that the teacher left the door propped open. But the Texas DPS corrected itself days later, telling ABC News that investigators have now determined that the teacher closed the door. McCraw said in testimony to the Texas Senate on June 21 that the locking mechanism was not engaged, though the teacher could not have known that from inside the building.

11:29 a.m.: Ramos hops a fence toward the school, surveillance video shows.

11:30 a.m.: Police receive the first 911 call detailing the crash and shots fired.

11:30 a.m.: The first police officer speeds past the gunman in car, surveillance video shows.

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, according to the Marshals.

11:31 a.m.: Funeral home footage shows the suspect shooting in between vehicles at the school.

11:31 a.m.: The suspect approaches the school through the parking lot, according to McCraw. Contrary to previous reporting, he does not encounter any officers outside of the building.

11:31 a.m.: Patrol vehicles arrive at the scene of the funeral home.

11:31 a.m.: A Uvalde ISD officer who heard the 911 call about a man with a gun drove immediately to the area, according to McCraw. 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, including some that went through a window, according to McCraw.

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. A boy leaves the bathroom and realizes the gunman is in the hallway before running away, surveillance video shows.

11:33 a.m.: 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.

The suspect shoots into classrooms 111 and 112 from the hallway. He then enters, exits and re-enters rooms 111 and 112.

The suspect fired more than 100 rounds at students and teachers, McCraw said. The two classrooms are connected internally. "Hundreds" of rounds are fired within his first four minutes in the classroom, McCraw said.

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, including two with rifles, McCraw said June 21. Two sustain "grazing wounds" from the gunman, who is firing down the hallway from behind a closed door, McCraw said.

11:36 a.m.: Two Uvalde Consolidated Independent School District Police officers, including Chief Pete Arredondo, and two Uvalde police officers enter the school through the south door, according to McCraw.

11:36 a.m.: Three Uvalde police officers and one UCISD officer enter the school through the west door, according to McCraw.

11:37 a.m.: Officers retreat after taking fire, surveillance video shows.

11:37 a.m.: Officer Ruben Ruiz, the husband of teacher Eva Mireles, checks his phone, surveillance video shows. Mireles had contacted Ruiz from the classroom, saying she had been shot and was dying, McCraw told the state Senate committee while testifying on June 21.

Ruiz was escorted off the scene, and his gun was taken away from him, McCraw said. The investigative report states that Ruiz did nothing wrong.

11:37 to 11:44 a.m: The shooter continues firing rounds at intervals, according to McCraw. Ramos entered the classroom with 315 cartridges, McCraw said, and fired 142 of them.

11:37 a.m.: Suspect gunfire injures officers approaching the classroom, McCraw said.

11:38 a.m.: Law enforcement-worn body camera shows an unknown officer say, "He's contained in this office," according to McCraw.

11:40 a.m.: Arredondo calls the Uvalde police landline, according to McCraw.

11:40 a.m.: School surveillance shows the suspect fire one round of gunfire, according to McCraw.

11:41 a.m.: Law enforcement body camera footage shows a Uvalde police officer say, "We believe that he is barricaded in one of the offices, there's still shooting," according to McCraw.

11:41 a.m.: Dispatch asks if the door is locked, to which a Uvalde police officer says, "I am not sure but we have hooligan [a door-entry device] to break it," law enforcement body camera footage shows, according to McCraw.

11:41 a.m.: Four first responders enter from the east hallway: two constables, a fire marshal and a Uvalde police officer, according to school surveillance, McCraw said.

11:42 a.m.: One DPS trooper and two Uvalde police officers enter from the east hallway, according to McCraw.

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.: Suspect fires one round of gunfire, according to school surveillance.

11:44 a.m.: A Uvalde police officer is heard saying, "Have some officers that are available get everybody back," according to body camera footage.

11:48 a.m.: UCISD Officer Ruben Ruiz, the husband of one of the teachers in the classroom, enters through the west door and is heard telling officers, "She says she's shot," according to body camera footage.

11:50 a.m.: An unknown officer says, "They need to get out of the hallway," to which another Uvalde police officer responds, "Chief is in there, chief in charge right now, hold on."

11:51 a.m.: Seven Border Patrol agents enter the school through the west door, according to McCraw.

11:52 a.m.: The first ballistic shield is brought into the school through the west door, according to school surveillance.

11:52 a.m.: A Uvalde police officer says on body camera footage, "Units just showing up, can you help with crowd control?"

11:53 a.m.: An unknown officer informs a DPS special agent that all they need right now is perimeter, according to body camera footage.

Someone comments on whether there are still kids inside, to which the DPS special agent responds, "If there is, then they just need to go in."

11:54 a.m.: A DPS special agent enters the building and is directed to where the suspect is located. He asks an unknown officer, "Are kids still in there?"

The unknown officer responds, "It is unknown at this time."

11:54 a.m.: A Uvalde police officer says, "He's in classroom 111 or 112. But chief is making contact with him. No one has made contact with him," according to body camera footage.

11:55 a.m. to noon Onlookers gather outside the school and grow restless and encourage officers to enter the building, according to a livestream video posted on social media.

11:56 a.m.: Conversation heard over body camera footage:
"Y'all don't know if there's kids in there?" an unknown officer asks.
"If there's kids in there, we need to go in there," a DPS special agent says.
"What's that?" an unknown officer says.
"If there's kids in there, we need to go in there," the DPS special agent says.
"Whoever is in charge will determine that," an unknown officer says.

11:56 a.m.: Someone heard on a Uvalde police channel recording says, "Again, it is critical for everybody to let PD take point on this."

11:58 a.m.: An unknown officer asks where the shooter is, and another officer responds, "The school chief of police is in there with him," Uvalde police recordings show.

11:58 a.m.: A DPS special agent says, "It sounds like a hostage rescue situation. Sounds like a [undercover] rescue, they should probably go in," according to body camera footage.

Approximately 11:58 a.m.: Video obtained by ABC News shows children escaping the school. This is not necessarily the first group of children to leave the school.

12:01 p.m.: A DPS special agent indicates he wants to go clear more rooms. An unknown officer responds, "Don't you think we should have a supervisor approve that?" to which the special agent responds, "He's not my supervisor," according to body camera footage.

12:03 p.m.: More officers arrive on scene and enter the building, according to McCraw. There was as many as 19 officers in the hallway at that time, McCraw said.

12:03 p.m.: A 911 call is made from a student in room 112 that lasts 23 seconds, according to an investigative report released by members of a special committee of the Texas state legislature on Sunday.

12:03 p.m.: A second ballistic shield is brought in the west door, according to school surveillance.

12:04 p.m.: A third ballistic shield is brought in the west door, according to school surveillance.

12:09 p.m.: A Uvalde police officer is heard saying, "Go around and get the master key to the rooms," according to body camera footage.

12:10 p.m.: The first group of deputy U.S. Marshals from Del Rio, nearly 70 miles away, arrives on site, according to the Marshals. Elements of a Border Patrol team begin arriving at the school.

12:10 p.m.: The first 911 caller calls back and says there are multiple dead in the classroom, according to McCraw.

12:11 p.m.: Arredondo requests a master key, according to body camera footage.

12:13 p.m.: The 911 caller calls again, according to McCraw.

About 12:13 p.m.: In a portion of a videotape obtained by ABC News from outside of Robb Elementary School, what appears to be a police radio dispatcher details a 911 call from a student inside room 112 who describes a room "full of victims."

12:14 p.m.: Arredondo gives instructions to officers to have a sniper on the east roof, according to body camera footage.

12:15 p.m.: U.S. Border Patrol tactical unit members arrive on scene, according to McCraw, with shields and other equipment.

12:16 p.m.: The 911 caller calls again and says eight to nine students are still alive, according to McCraw.

Arredondo is recorded saying, "I just need a key," according to body camera footage.

12:17 p.m.: Uvalde Consolidated Independent School District announces the shooting on Twitter.

12:17 p.m.:: "Tell them to f------ wait. No one comes in," Arredondo is recorded saying, according to body camera footage.

12:18 p.m.: Tear gas canisters are dropped off, surveillance video shows.

12:19 p.m.: Multiple officers put on tear gas masks, while others make phone calls, surveillance video shows.

12:19 p.m.: A call is made by someone else from room 111. The caller hangs up when another student tells her to, McCraw said.

12:20 p.m.: A fourth ballistic shield is brought into the school through the west door, according to school surveillance. The last shield, supplied by the U.S. Marshals, was rifle-rated and therefore would have been the only one with meaningful protection to officers against the attacker's AR-15-style rifle, according to the report. The committee received no evidence that anyone told Arredondo or anyone else on the south side of the building about the arrival of the rifle-rated shield, the report states.

12:21 p.m.: The gunman fires again at the classroom door, according to McCraw, forcing officers in the building to reposition themselves down the hallway away from the door.

12:21 p.m.: The person in room 111 calls 911 again and three shots are heard over the call.

12:21 p.m.: According to school surveillance, the suspect fired four rounds of gunfire.

12:21 p.m.: "Can you go get a breaching tool? Like for a trailer house?" Arredondo is heard saying over body camera footage.

12:23 p.m.: In body camera footage, Arredondo is heard saying: "We've lost two kids. These walls are thin. If he starts shooting, we're going to lose more kids. I hate to say we have to put those to the side right now."

12:24 p.m.: Arredondo tries to communicate through the wall with the gunman in Spanish and English.

12:25 p.m.: A female victim appears to tell a police dispatcher, "I got shot!" according to audio overheard in the background of a Facebook livestream video cleared and verified by ABC News.

12:26 p.m.: An unknown officer is heard on body camera saying, "There's a teacher shot in there," to which a Uvalde police officer responds, "I know."

12:27 p.m.: Arredondo is heard saying, "People are going to ask why we're taking so long. We're trying to preserve the rest of the life," according to body camera footage.

12:27 p.m.: Arredondo is heard saying, "Do we have a team ready to go? Do we have a team ready to go? Have at it," according to body camera footage.

12:28 p.m.: "There is a window over there obviously. The door is probably going to be locked. That is the nature of this place. I am going to get some more keys to test," Arredondo says, according to body camera footage.

12:28 p.m.: "These master keys aren't working here, bro. We have master keys and they're not working," Arredondo says, according to body camera footage.

Around 12:30 p.m.: Various officers entered through the south door and walked by Arredondo and Coronado, who were stacking up south of Rooms 111 and 112, on the west side of the hallway, anticipating a move to breach the classrooms, according to the report, citing Coronado's body-worn camera.

12:30 p.m.: "OK. We've cleared out everything except for that room. We still have people down there just past the flag to the right. But, uh, we're ready to breach but that door is locked," Arredondo says, according to body camera footage.

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," according to Broadcastify audio.

12:33 p.m.: "I say we breach through those windows and shoot his f------ head off through the windows," Arredondo says, according to body camera footage.

12:34 p.m.: Someone asks, "We don't know if he has anyone in the room with him, do we?" to which Arredondo responds, "I think he does. There's probably some casualties," Uvalde Police Sgt. Daniel Coronado's body camera footage shows, according to the report.

12:35 p.m.: A hooligan breaching tool is brought into the building through the west door.

12:36 p.m.: An officer is seen stopping to tie his shoe, surveillance video shows.

12:36 p.m.: Another 911 call is made by the initial caller and it lasts for 21 seconds, according to McCraw. 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.

12:37 p.m.: A stretcher is brought into the hallway, surveillance video shows.

12:38 p.m.: Arredondo attempts again to communicate with the suspect in English and Spanish.

12:41 p.m.: "Just so you understand, we think there are some injuries in there. And so you know what we did, we cleared off the rest of the building so we wouldn't have anymore besides what's already in there, obviously," Arredondo says, according to body camera footage.

12:42 p.m.: "We're having a f------ problem getting into the room because it is locked. He's got an AR-15 and he's shooting everywhere like crazy. So, he's stopped," Arredondo says, according to body camera footage.

12:43 p.m.: "They gotta get that f------ door open, bro. They can't get that door open. We need more keys or something," Arredondo says, according to body camera footage.

12:43 p.m.: The 911 caller inside room 112 asks for police to be sent in, according to McCraw.

12:46 p.m.: "If y'all are ready to do it, you do it, but you should distract him out that window," Arredondo says, according to body camera footage.

12:46 p.m.: The 911 caller inside room 112 says she can hear police officers next door, according to McCraw.

12:47 p.m.: The 911 caller inside room 112 again asks for police to be sent in, according to McCraw.

12:47 p.m.: A sledgehammer is brought in from the east hallway, according to school surveillance.

12:47 p.m.: A person wearing a stethoscope around the neck and purple gloves appears to give instructions, surveillance video shows.

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 classroom 111, sources told ABC News. Officers then immediately engage in a "rescue operation," Escalon said

McCraw said at a June 21 hearing that the classroom door was never locked throughout the incident.

12:50 p.m.: One officer says, "Wait!" and holds back other officers from entering the classroom, surveillance video shows.

1:06 p.m.: Police report that the suspected shooter was killed by officers at the scene after they broke into the classroom.

In total, 376 law enforcement officers responded to the tragedy at Robb Elementary School, according to an investigation from the Texas House of Representatives.

ABC News' Lucien Bruggeman, Matthew Fuhrman and Will Steakin contributed to this report.