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

When federal agents from Customs and Border Protection and Homeland Security Investigations arrived at Robb Elementary School Tuesday, they immediately encountered a scene of confusion and chaos, according to multiple law enforcement officials briefed on the attack.

Some arrived with heavy equipment, others with whatever they could carry as they ran to the scene on foot.

Initially, these agents, multiple law enforcement sources told ABC News, tried to discern who was doing what, where was shooter who was engaging law enforcement and how were children were being evacuated.

Once the tactical team assembled with enough gear, they became aware of an order not to enter the classroom because they were told the suspect had barricaded himself, the sources told ABC News.

The Texas Department of Public Safety has said the incident commander wrongly believed the shooting had stopped.

Eventually, the special agent-in-charge of Homeland Security Investigations gave the instruction to all federal agents under the umbrella of the Department of Homeland Security that they were free to use their best judgment and to do what they felt was best, the sources said.

The federal agents were unsure whether any children could be saved at that point, but they were interested in evacuating the wounded. Some agents brought children in other classrooms out through windows.

The tactical team went in at 12:50 p.m. CDT and fatally shot the suspect, 77 minutes after the shooting started, officials said.

The suspect was dead at the scene, the sources said. He was found with more than a dozen bullet wounds.