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

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

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

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

A fourth-grade teacher and a 10-year-old boy were among those killed, ABC News has learned.

The teacher, Eva Mireles, had worked in the school district for approximately 17 years, her aunt, Lydia Martinez Delgado, confirmed to ABC News.

Fourth-grader Xavier Lopez was among the 19 children killed.

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