Alleged school shooter Salvador Ramos was in the classroom for 77 minutes before officers entered and killed him. During that time, he discharged 315 rounds of ammunition, with hundreds of those rounds fired within the first four minutes of his arrival, authorities said.

After the initial barrage, the police commander on the scene mistakenly believed the shooter was barricaded and it was no longer an active shooter incident, Texas Department of Public Safety Director Steve McCraw told reporters in an update Friday. But as officers gathered outside the classroom, the gunman kept shooting on at least six occasions, the new details show.

At 11:35 a.m., as the first three officers entered the building and approached classrooms 111 and 112, the suspect fired into the hallway through a closed door, where two officers sustained "grazing wounds," McCraw said.

He fired an additional 16 rounds two minutes later -- at 11:37 a.m. -- and again at 11:38 a.m., 11:40 a.m. and 11:44 a.m., according to McCraw, who did not specify whether the additional discharges were directed at officers in the hallway or at those inside the classrooms.

At 12:21 p.m., with as many as 19 officers then gathered outside the classroom, the suspect again fired at the closed door, forcing officers to "move down the hallway," McCraw said.

Despite those additional spurts of gunfire – and a 911 call from inside one of the classrooms alerting a dispatcher that eight or nine people remained alive -- officers did not enter the classroom and kill Ramos until 12:50 p.m., according to McCraw.

The police response to the shooting is now being investigated, Texas Gov. Greg Abbott said Friday.

-ABC News' Lucien Bruggeman

The Uvalde Consolidated Independent School District in Texas hosted active shooter training for its six-member police force two months prior to the massacre at Robb Elementary, based on the "Active Shooter Response for School-Based Law Enforcement" course from the Texas Commission on Law Enforcement, which explicitly states: "First responders to the active shooter scene will usually be required to place themselves in harm's way and display uncommon acts of courage to save the innocent."

The course manual also includes this sobering instruction: "A first responder unwilling to place the lives of the innocent above their own safety should consider another career field."

The training makes clear the "first priority is to move in and confront the attacker."
It is "safer" and "preferable" to have a team of at least four officers move on a subject but, since "time is the number one enemy during active shooter response," even a single officer is expected to act, according to the training document.

In Uvalde, 19 officers entered the school but remained in the hallway, Texas Department of Public Safety Director Steven McCraw said at a press conference Friday.

Only when an attacker is isolated and "can do no more harm to students, staff, or visitors" is the officer not obligated to enter the room, which is what McCraw said the incident commander, Uvalde ISD Chief Pete Arredondo, believed.

"It was the wrong decision," McCraw said.

-ABC News' Mike Levine and Aaron Katersky

The district attorney in Uvalde County told ABC News Friday she would make charging decisions once an investigation into the law enforcement conduct in connection with the deadly shooting at Robb Elementary School is complete.

The district attorney, Christina Mitchell Busbee, declined to answer questions about specific individuals or conduct.

The comments come after the Texas Department of Public Safety provided more details about the delayed response to Tuesday's active shooter incident.

During a press briefing Friday, Texas Gov. Greg Abbott said he would like to know why the Uvalde Consolidated Independent School District police chief did "not choose the strategy that would have been best to go in there." He said he does not know if the chief is still on active duty.

The superintendent of the Uvalde school district declined to answer questions about the police chief during the briefing.

-ABC News' Aaron Katersky and Josh Margolin

Texas Gov. Greg Abbott said he was "misled" about the response to the Uvalde school shooting.

"I am livid about what happened," Abbott said during a press briefing Friday, hours after the Texas Department of Public Safety detailed missteps that led to a 35-minute wait to breach the classroom where the shooter was.

"As everybody has learned, the information that I was given turned out, in part, to be inaccurate, and I'm absolutely livid about that," Abbott said Friday. "There are people who deserve answers the most, and those are the families whose lives have been destroyed. They need answers that are accurate, and it is inexcusable that they may suffer from any inaccurate information whatsoever."

The governor said there will be investigations into the release of information on the shooting and the strategy employed in the response.

On Wednesday, Abbott said an officer had confronted the shooter at the entrance to the school building, which was not the case.

"But the reality is, as horrible as what happened, it could have been worse," he also said at the time. "The reason it was not worse, is because law enforcement officials did what they do."

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.”