(UVALDE, Texas) -- A small town in rural Texas is reeling after a gunman opened fire at an elementary school on Tuesday, killing 19 children.
Two teachers were also among those killed at Robb Elementary School in Uvalde, according to authorities.
Prior to opening fire at the school, the suspect also allegedly shot his grandmother, officials said.
The alleged gunman -- identified by authorities as 18-year-old Salvador Ramos, a student at Uvalde High School -- is dead.
Here's how the news is developing. All times Eastern:
May 26, 6:49 pm
Law enforcement examining if lockdown was audible to students, staff: Sources
The response by school officials and law enforcement is becoming a key focus in the ongoing investigation into the Uvalde school shooting, law enforcement sources told ABC News Thursday.
It is unclear whether any students and teachers heard an official call for a lockdown once the gunman entered the building, the sources said.
Additionally, investigators are looking into whether officers on site could have made other attempts to enter the school to end the gunman’s rampage faster, the sources said. Responding police were met with gunfire and called for tactical teams with proper equipment to enter the classroom and neutralize the gunman, according to the sources.
-ABC News' Matt Gutman, Josh Margolin, Aaron Katersky and Luke Barr
May 26, 6:19 pm
10-year-old survivor recalls moments after hearing shots fired
A student who was in the classroom next door to the one the gunman entered recounted to ABC News what she did next.
Gemma Lopez, 10, said she heard five to six gunshots and commotion outside her classroom at Robb Elementary School before a bullet whizzed by her arm and into the wall. She recalled seeing a puff of smoke, which is when she knew they were all in danger.
She said she turned off the lights and then ducked under the tables -- what she learned to do in the active shooter training she has undergone since kindergarten. There were no locks inside and they did not have a key in the classroom to lock the door from the inside, she said.
Authorities yelled at the gunman to put down his weapon, to which he reportedly shouted in response, "Leave me alone please," in Spanish, Gemma recalled.
Gemma said her best friend, Amerie Jo Garza, was one of the 19 children killed in the massacre.
-ABC News' Matt Gutman and Olivia Osteen
May 26, 6:15 pm
Accused gunman sent concerning messages to more than a dozen people before school massacre
The accused Robb Elementary School shooter appears to have sent disturbing messages -- including claims about intentions of violence at schools -- to numerous young people online in the days and weeks before the shooting, ABC News has found.
Over a dozen people told ABC News that the accused gunman, 18-year-old Salvador Ramos, sent them concerning messages across multiple social media platforms in the days leading up to the massacre.
Hours before the massacre, the gunman allegedly messaged a young girl on Instagram warning that he had a secret he wanted to tell her, according to messages reviewed by ABC News, which law enforcement sources say are part of the ongoing investigation into the shooter. He had tagged her in a photo of two guns days earlier.
In another alleged message the morning of the shooting, Ramos sent 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. She replied asking, “Why'd u send me a pic of a gun."
And moments before the attack, the accused gunman 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.
Another young user told ABC News the shooter was on Yubo the day before the massacre and implied something would occur the next day, the day of the shooting.
-ABC News' Will Steakin and Olivia Rubin
May 26, 4:19 pm
Shooter carried 7 30-round magazines, 15 more found in backpack
The Robb Elementary School gunman had a total of seven 30-round magazines with him in the classroom where the shooting took place, multiple law enforcement sources told ABC News.
One 30-round magazine was in the AR-15-style rifle used in the shooting and six magazines were carried on a tactical vest worn by the shooter, with the potential to hold 210 rounds.
It is unclear how many rounds were expended.
Fifteen additional loaded magazines, potentially holding 450 rounds, were found in a backpack that police said the shooter had when he exited a pickup truck that he crashed near the school.
It is unclear where this backpack was found by police or whether he had it in the classroom.
-ABC News' Jack Date, Luke Barr, Josh Margolin and Pierre Thomas
May 26, 4:07 pm
Biden, first lady to visit Uvalde on Sunday
The White House announced that President Joe Biden and first lady Jill Biden will visit Uvalde, Texas, on Sunday.
They will travel to Uvalde "to grieve with the community," the White House said in a statement.
-ABC News' Jon Garcia
May 26, 3:32 pm
Texas official gives updated timeline of shooting
Even though the school doors were supposed to be locked during the day, it appears the door the gunman entered through was unlocked, Victor Escalon, the Texas Department of Public Safety's regional director for south Texas, said at a press conference Thursday.
Escalon gave an updated timeline of the shooting:
After crashing his car, the gunman got out through the passenger side with a rifle and bag containing ammunition.
The suspect walked around then saw two witnesses at the funeral home across the street from where he crashed his car and opened fire on them. Neither person was struck.
While in the parking lot, the gunman fired shots at the school multiple times. The suspect then walked into the west side of the building, Escalon said.
The Uvalde Police Department and the Independent School District Police Department attempted to enter the school building four minutes later, but they heard gunfire and took rounds so they moved back, took cover and called for additional resources, Escalon said.
Escalon said the officers "don’t make entry initially because of the gunfire they’re receiving. But we have officers calling for additional resources."
While they made calls to bring in backup, officers evacuated students and teachers.
Approximately an hour later, U.S. Border Patrol tactical teams arrived, made entry and shot and killed the suspect, Escalon said.
Escalon said it then became a rescue operation.
May 26, 2:56 pm
Texas official says gunman not confronted by officer before entering through unlocked door
Texas 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.
Police believe the gunman was able to get into the building through an unlocked door at the back of the school, said Victor Escalon, the Texas Department of Public Safety's regional director for south Texas.
The gunman was shot and killed by Border Patrol tactical team nearly an hour after the shooting began, Escalon said.
May 26, 2:37 pm
Uvalde police says 'officers responded within minutes,' amid criticism of response to shooting
Uvalde police officers responded to the shooting "within minutes," Uvalde police said in a statement Thursday.
"Our personnel have displayed the upmost commitment to our community during this difficult time as we all are suffering as members of the community, that is the family of Uvalde. It is important for our community to know that our Officers responded within minutes alongside Uvalde CISD Officers," Daniel Rodriguez, Uvalde chief of police, said in a statement.
"I understand questions are surfacing regarding the details of what occurred. I know answers will not come fast enough during this trying time, but rest assured that with the completion of the full investigation, I will be able to answer all the questions that we can."
Rodriguez added, "I know words will never ease the pain that we are all suffering, but I hope you will join me in taking some solace in knowing that the pain comes from the fact that we all have such deep love for all the victims who have been taken from us, those who are recovering, and those who only time and love will continue to heal."
May 26, 2:11 pm
Husband of teacher killed in shooting dies of heart attack
Joe Garcia, the husband of teacher Irma Garcia who was killed in the shooting, died of a heart attack on Thursday, according their nephew and a close family friend.
The two were set to celebrate their 25th anniversary this year. The couple had four children.
-ABC News' Alondra Valle
May 26, 1:55 pm
Mother of victim fatally shot says she 'lost a piece of my heart'
Eva Dulia Orta, the mother of 10-year-old Rojelio Torres, a fourth grader who died in the Tuesday shooting at Robb Elementary, told ABC News that she is trying to stay strong for the rest of her children, but "I lost a piece of my heart," she said.
The mother of four told ABC News she went to pick up two of her children at the school, but only came home with one.
This has not only devastated her entire family, but the community, she said, speaking with her twin sister.
"We are praying for everyone, all the children and all the families," she said.
-ABC News' Maria Elena Salinas
May 26, 1:49 pm
Witness recounts police response to Uvalde shooting: 'Why aren't they going in?'
Bob Estrada, who lives across the street from Robb Elementary School, recounted to ABC News the moments he went out on his porch after hearing gunshots, saying he witnessed the police response to the shooting unfold.
Estrada, whose grandson is a second grader at the school who survived the shooting, said he saw "quite a few" officers outside the school immediately, and then police cars started driving up -- but "some of them just stood there."
"Why aren't they going in?" Estrada told ABC News he wondered at the time.
Estrada said it was not long before parents began to arrive. "They were hysterical," he said.
"There were parents out there, and they were kinda motioning like they wanted to come in," Estrada said. "They were motioning like, 'What are you doing? Go in!'"
Estrada said he did see some officers go in immediately.
Asked if he saw reinforcements heading into the school, Estrada said no. But, he did not know what sort of presence may have already been inside.
-ABC News' Matt Gutman, Olivia Rubin, Jeffrey Cook and Laura Romero
May 26, 1:24 pm
Young girl who gunman allegedly texted before shooting speaks out
The young girl who allegedly received messages from the Texas gunman moments before his rampage told ABC News she has been asking herself "what if I could change the outcome" since seeing the news that her friend killed 19 students and two teachers on Tuesday.
"Ever since May 24th I have been guilt tripping myself, what if I could change the outcome, what if I could change his mind to not do this. I was too dumb to realize why he bought two Rifles on his birthday May 16th and ordered a package full with ammunitions not knowing what he was going to do with it," the 15-year-old girl, who asked to be referred to as "Cece," told ABC News.
The messages are part of an ongoing investigation into the shooter, law enforcement sources told ABC News.
Cece, who lives in Germany, said she met the accused gunman on the social media app Yubo where they would "join each others live" streams. The pair met on the app on May 9 before exchanging cellphone numbers, Cece said.
The messages reviewed by ABC News and other outlets appear to show that Cece did not respond to the gunman's threats until after news of the shooting broke and nearly all the texts are solely from the suspect. It is unclear if the messages were at all edited.
-ABC News' Will Steakin
May 26, 10:01 am
Texas school district cancels school after receiving 'credible threat of violence'
The Donna, Texas, Independent School District has canceled classes after it received a "credible threat of violence," school officials said in a letter posted on Facebook. Donna is about 4 1/2 hours from Uvalde.
The threat is currently under investigation and classes will resume on Tuesday, the district said.
"In light of the recent events and in an abundance of caution we will be canceling school district-wide and staff will be working from home," the letter said. "The safety and security of our students & staff is our first priority."
-ABC News' Luke Barr
May 26, 7:32 am
Bodies of nine victims released to funeral homes, with more expected today
Nine of the deceased victims' bodies were released to funeral homes in Uvalde on Wednesday evening, Uvalde County Justice of Peace Eulalio Diaz told CNN.
More -- possibly all -- of the remaining bodies are expected to be released at some point on Thursday, according to Diaz. It will mark the beginning of the funeral arrangement process for many grieving families in the wake of the second-deadliest school shooting in U.S. history. There are two funeral homes in Uvalde, and both are offering free services to families of the victims.
"My job is to try and get them back home as quickly as possible," Diaz told CNN in an interview early Thursday.
In a county of less than 50,000 people, there is no medical examiner and the justice of the peace in the state of Texas assumes the responsibility of the county coroner, according to Diaz.
Diaz described his job of going in and assessing the bodies of the dead at Robb Elementary School on Tuesday in the immediate aftermath of the mass shooting. He said Irma Garcia, one of the teachers who were killed, was a former high school classmate of his.