The gunman warned about the shooting in private messages on Facebook minutes beforehand, a spokesperson for Meta said Wednesday. The warning on Facebook was made in "private one-to-one text messages that were discovered after the terrible tragedy occurred."

The gunman sent three messages on Facebook about 30 minutes before the shooting saying: "I'm going to shoot my grandmother," "I shot my grandmother" and "I'm going to shoot an elementary school," Texas Gov. Greg Abbott said at a press conference.

Abbott said the suspect was reportedly a high school dropout. Officials have reportedly not identified a criminal history for the suspect, but Abbott said he may have had a juvenile record, but that is yet to be determined.

Abbott said the suspect did not have a known mental health history.

According to the ATF, the shooter made his gun purchases on two separate days: May 17 and May 20.

Beto O'Rourke, a candidate running for governor of Texas, interrupted a press conference held by current Gov. Greg Abbott Wednesday, shouting at Abbott before being escorted from the building.

O'Rourke protested the current governor's stance on gun control.

"You are doing nothing!” he shouted.

Six people injured in the Texas elementary school shooting remain hospitalized on Wednesday.

Three children and one adult are at the University Hospital in San Antonio, two of whom are in serious condition.

Two other adults are hospitalized at Brooke Army Medical Center, both in serious condition.

All patients treated at Uvalde Medical Center have been discharged. The hospital said it treated 15 individuals, 11 of whom were children. Three of those 11 children were transferred to other hospitals in San Antonio and eight were discharged home.

The four remaining patients were adults, one was transferred to another hospital and three were discharged home.

-ABC News' Jennifer Watts

Jacinto Cazares, the father of Jacklyn Jaylen Cazares, a 10-year-old killed in the Texas elementary school shooting, told ABC News he blames the school and police for the massacre, not the murder weapons.

"I want to say we hold the school responsible for not having locked doors and no protocol, no training. Also the Police for not having a better and faster tactical response time. There was at least 40 lawmen armed to the teeth, but didn't do a darn thing till it was far too late," Cazares told ABC News in a statement.

He added, "The situation could've been over quick if they had better tactical training and we as a community witnessed it first hand. I'm a gun owner and I do not blame the weapons used in this tragedy. I'm angry how easy it is to get one and young you can be to purchase one."

-ABC News' Miles Cohen

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.”