The videos show a chaotic scene. A bunch of officers are seen holding a perimeter around the campus and pushing panicked parents back. Some staff members are leading kids out of the school. At one point, officials tried to load children into school buses to lead them away from the active area, but the bus is left unattended, and one boy climbs out of a half-opened window and into their arms.

Officials will look at whether officers could have arrived sooner to the school. Castro called for the review to be handled by the FBI to clear up conflicting accounts of local authorities.

It is a small town, and you have to understand that, according to the man.

The best practices for active shooter situations include attempting to confront the shooter immediately in order to reduce the number of injured and casualties.

The purpose of law enforcement is to stop the active shooter as soon as possible, according to a Department of Homeland Security pamphlet.

Policies and procedures developed by law enforcement agencies allow for lone officers to confront perpetrators if they see an opportunity in active-shooter scenarios. According to a report from the Police Executive Research Forum, most of the agencies that require a team to be assembled consist of small teams of four to five officers.

The teams are often told not to attend to injured victims, but to seek out and destroy the shooter as soon as possible.

The policy of waiting for the police to arrive before entering an active shooter situation has been scrapped by many police departments since the 1999 school shooting in which more than 15 people were killed.

The lieutenant from the Texas Department of Public Safety defended the decision to wait for tactical teams to confront the shooter on CNN.

He told CNN that officers kept cover because they were shot at, and that they were able to contain the shooter in one classroom.

The classroom was filled with most of the victims, but the officers risked being shot themselves and the shooter moving to another part of the school if they confronted him earlier.

There is a good chance that the shooter would have made it to other classrooms and killed more people. They could have been shot if they proceeded any further without knowing where the shooter was. They could have been killed.

A video on social media from Tuesday shows parents waiting outside the school for police to arrive, angrily asking why they weren't rushing in, with some even trying to get into the school.

He heard rumors of parents confronting police outside the school, but he could not confirm the reports.

One parent was put in handcuffs after urging police to go in.

Parents are in a video urging police to go in while an officer pushes them back. When a parent asks why police aren't trying to save their kids, the officer responds: "Because I'm having to deal with you!"