At a press conference on Friday, Texas Department of Public Safety Director Steven McCraw acknowledged that officers on the scene in the small rural town of Uvalde Tuesday miscalculated what was unfolding.
"It was not the right decision. It was the wrong decision. Period ... We believe there should have been an entry. We don't have time," he said.
Children were inside the Robb Elementary School classroom with him, making 911 calls, McCraw said in a press conference Friday. By the time a U.S. Border Patrol tactical team arrived and killed the alleged shooter, identified as Salvador Ramos, 19 children, and two teachers were killed, several more were severely injured, and others survived to recount the nightmare.
WATCH: Boy who survived Texas school shooting recalls gunman saying 'you're all gonna die'
He 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, according to authorities.
What we know about the police response
Relatives of victims and neighbors of Uvalde's Robb Elementary School are raising questions over how police officers who first arrived on the scene handled the situation -- including whether they followed their own training.
Officials said around 11:28 a.m., the suspect crashed his grandmother's car on the perimeter of the school, pulled out an AR-style rifle and backpack filled with ammunition, and fired at two nearby witnesses as he made his way toward the school. Prior to arriving at the school, the suspect also allegedly shot his grandmother, officials said.
WATCH: Law enforcement officials admit 'mistakes were made'
Officials said Thursday that police did not confront the gunman before he entered the school, despite earlier reporting that a school district police officer had confronted the gunman.
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At 11:33 a.m., soon after the gunman entered the school through a door that had been propped open, he entered two classrooms and fired at least 100 rounds, McCraw said. Within a few minutes, seven Uvalde police officers were inside the school, and two were grazed by bullets, McCraw said.
A tactical team from Customs and Border Protection was on scene at 12:15 p.m., but did not breach the classroom until 12:50 p.m. -- after a janitor provided keys to unlock the door, McCraw said.
TIMELINE: A look at Uvalde shooter's movements day of massacre
The incident commander believed he was dealing with a barricaded subject inside the school and the children were not at risk, McCraw said.
On Tuesday, a spokesperson for the DPS, Lt. Chris Olivarez, said on national TV that at one point on Tuesday, police officers on the scene decided to "focus" on evacuating students and teachers "around the school," instead of racing to the shooter's location -- even as they heard more gunshots.
Videos posted online show angry parents outside the school, urging police officers to take more action.
MORE: Onlookers urged police to charge into Texas school after shooting began, witnesses say
Those inside a classroom with the shooter made several calls to 911 as the tactical unit waited 35 minutes outside.
Robb Elementary School survivor Samuel Salinas, 10, recounted those moments of horror to "Good Morning America," saying the gunman came into his classroom, closed the door, and told them, "You're all going to die," before opening fire.
"He shot the teacher and then he shot the kids," Salinas said, recalling the cries and yells of students around him.
Salinas said he and other children pretended to be dead "so he wouldn't shoot."
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A 911 call was made at 12:03 p.m. from room 112 and lasted 23 seconds. McCraw did not identify the caller. She called back at 12:10 p.m. and advised that there were multiple deaths in the classroom, McCraw said.
The person then called again at 12:13 p.m. and again at 12:16 p.m., when said there were eight to nine students who were still alive, McCraw said. A call was made by someone else from room 111 at 12:19 p.m., the caller hung up when another student told her to hang up, McCraw said.
At 12:21 p.m., three shots were heard over a 911 call. At 12:36 p.m., another 911 call was made by the initial caller and it lasted for 21 seconds. The student caller was told to stay on the line and be very quiet. She told 911 that the gunman shot the door, McCraw said. At approximately 12:43 p.m. and 12:47 p.m., she asked 911 to please send the police now, McCraw said.
The caller said she could hear police next door at 12:46 p.m. At 12:50 p.m., the Border Patrol tactical unit finally breached the door and shot the suspect.
Who are the victims?
A fourth-grade teacher, several sets of cousins, and a 10-year-old boy whose family called him "the life of the party" were among those killed in the mass shooting Tuesday, ABC News has learned.
The husband of one of the teachers killed also died two days later from a heart attack. The couple was set to celebrate their 25-year anniversary.
"When parents drop their kids off at school, they have every expectation to know that they're going to be able to pick their child up when that school day ends. And there are families who are in mourning right now," Gov. Greg Abbott told reporters.
ABC News has confirmed the identities of the following victims:
- Eva Mireles, teacher
- Xavier James Lopez, 10
- Amerie Jo Garza, 10
- Rojelio Torres, 10
- Jayce Carmelo Luevanos, 10
- Jailah Nicole Silguero, 11
- Eliahana Cruz Torres
- Annabell Rodriguez, 10
- Jacklyn Jaylen Cazares, 10
- Irma Garcia, teacher
- Uziyah Garcia
- Alithia Ramirez
- Makenna Lee Elrod, 10
- Ellie Garcia
- Nevaeh Bravo, 10
- Tess Mata
- Alexandria Aniyah Rubio
- Layla Salazar
- Maite Rodriguez
- Jose Flores
- Maranda Mathis
Who is Salvador Ramos?
Authorities shed more light on some of the suspect's digital footprint in the weeks and months before Tuesday's mass shooting.
In September 2021, suspected gunman Salvador Ramos, a student at Uvalde High School, asked his sister to buy him a gun and she "flatly refused," McCraw said.
On Feb. 28, in an Instagram group chat with four people, they discussed "Ramos being a school shooter," McCraw said. The next day, on March 1, in an Instagram chat with four people, Ramos discussed buying a gun, according to McCraw.
Additionally, over a dozen people told ABC News that Ramos sent them concerning messages across multiple social media platforms in the days leading up to the massacre.
Moments before the attack, he allegedly sent a string of messages to a young girl he met online, detailing that he had shot his grandmother and was heading to the school for his next target, according to messages reviewed by ABC News.
His mother, Adriana Reyes, told ABC News' Chief National Correspondent Matt Gutman that her son was "not a monster," but that he could "be aggressive."
"I had an uneasy feeling sometimes, like 'what are you up to?" Reyes said. "He can be aggressive... If he really got mad."
WATCH: Mother of Texas school shooting suspect speaks out; new text messages raise questions
Some classmates told ABC News that Ramos was known for fighting and threatening fellow students. They said he exhibited increasingly disturbing behavior over the past two years, threatening at least one classmate and stalking others, and that he claimed to have cut scars into his face.
Survivors try to move forward
Uvalde is reeling days after facing the second deadliest school shooting in American history, setting up memorials across the community and gathering in prayer. President Joe Biden and first lady Jill Biden will travel to Uvalde Sunday to pay tribute to the victims.
While authorities piece together a motive for the shooting rampage, survivors are trying to move forward.
The memorial is growing for all 21 victims whose names are now etched in white crosses outside the school.
The distraught families are taking on the difficult task of making arrangements for their loved ones.
The only two funeral homes in Uvalde are both offering free funeral services to victims of the shooting.
Since 2013, the year after the mass shooting at Sandy Hook Elementary School in Newtown, Conn., mass shootings in the United States -- described as shooting incidents in which at least four people are injured or killed -- have nearly tripled. Already, there have been 213 mass shooting incidents in 2022 -- a 50% increase from 141 shootings by May 2017 and a 150% increase from 84 by May 2013. The graphic above shows the number of shooting incidents per state. Mobile users: Click here to see our map of mass shootings in the US since Sandy Hook.