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

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.

-ABC News Ahmad Hemingway

There were four Border Patrol agents, members of elite specialized units, who engaged and stopped the elementary school shooter, along with state and local officers, a Customs and Border Protection official told ABC News.

One agent, who was part of the Border Patrol Tactical Unit, or BORTAC, held a shield as the group pushed toward the gunman's incoming fire, the official said.

Two BORTAC agents discharged their weapons along with one member of the Border Patrol's Search, Trauma and Rescue unit -- all part of the group of four.

At least one BORTAC agent shot the gunman, although it's unclear who among them killed him, the official said.

-ABC News' Jack Date and Quinn Owen

Moments before carrying out the deadly attack at Robb Elementary, the suspected 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.

The messages allegedly show the accused gunman, 18-year-old Salvador Ramos, texting with a 15-year-old in Germany who he met on the social media platform Yubo, describing an argument he was having with his grandmother over a phone bill before texting, "I shot my grandmother in the head" and "ima go shoot up a elementary school rn."

"She's on the phone with AT&T," Ramos allegedly wrote at 11:06 a.m., while referring to his grandmother with a derogatory term.

"Ima do something to her rn," he said in another alleged message. Minutes later, the gunman allegedly wrote, "I shot my grandmother in the head" before immediately adding "ima go shoot up a elementary school rn."

The friend did not reply to the accused gunman's messages until news broke regarding the shooting, according to the screenshot reviewed by ABC News.

Speaking to The New York Times, the girl said she only asked a friend in the United States about contacting law enforcement after she saw news of the shooting, telling The Times, “Maybe I could’ve changed the outcome... just could never guess that he’d actually do this.”

Law enforcement sources tell ABC News the messages are part of the ongoing investigation into the shooter.

-ABC News' Will Steakin, Josh Margolin and Aaron Katersky

The Justice Department will conduct a critical incident review to examine the law enforcement response to last week’s school shooting in Uvalde, Texas, a spokesperson announced on Sunday.

The review is being conducted at the request of Uvalde Mayor Don McLaughlin and the DOJ will publish a report on its findings at the conclusion.

"The goal of the review is to provide an independent account of law enforcement actions and responses that day, and to identify lessons learned and best practices to help first responders prepare for and respond to active shooter events. The review will be conducted with the Department’s Office of Community Oriented Policing," the DOJ said in a statement.

“As with prior Justice Department after-action reviews of mass shootings and other critical incidents, this assessment will be fair, transparent, and independent. The Justice Department will publish a report with its findings at the conclusion of its review.”