(CNN) — The chairman of the Texas House committee investigating the Uvalde school shooting is pushing for the release of hallway surveillance video that shows what police were doing as a gunman remained inside adjoining classrooms for about 77 minutes.

Rep. Dustin Burrows, the committee chairman, said Monday that releasing the hallway footage would be important because the public would see the evidence for themselves.

“I can tell people all day long what it is I saw, the committee can tell people all day long what we saw, but it’s very different to see it for yourself, and we think that’s very important,” he said.

Burrows is prohibited from releasing the hallway video because he signed a non-disclosure agreement with the Texas Department of Public Safety, he said on Twitter on Friday. He attached two letters to his tweet. In one, he asked the DPS for permission to release the video to the public. The other is a response from the DPS saying that the agency agrees that the video will bring “clarity to the public regarding the tragic events in Uvalde,” but adds the Uvalde district attorney “has objected to releasing the video.”

His tweet states that the video he is pushing to release “contains no imagery of victims or footage of violence.”

Burrows also said the committee is looking to release a preliminary report on the shooting “sooner than later.” The report could be released within the next 10 days, a source close to the committee had previously said.

The video would offer primary evidence of what responding police were doing when a gunman opened fire inside adjoining elementary school classrooms on May 24, fatally shooting 19 young students and two teachers. A group of officers waited in a nearby hallway for over an hour before they breached the door and killed the gunman.

What officers were doing in those 77 minutes remains largely unclear, and some officials have questioned the trustworthiness of the various investigations working to understand what went wrong that day.

Last month, DPS Director Col. Steven McCraw criticized that delay as an “abject failure,” in part citing evidence from the hallway surveillance video.

What the video shows

Some images from the video were obtained by the Texas Tribune and Austin American-Statesman and showed that officers had tactical gear and significant firepower — including rifles and a tactical shield — well before they ultimately breached the door.

The video is “wrenching,” Tony Plohetski, a reporter for the Austin American-Statesman who has watched the surveillance footage told CNN.

The video begins shortly after the gunman entered the school at 11:33 a.m. In the video, the 18-year-old gunman enters a classroom and “you hear a hail of gunfire,” Plohetski said. Minutes later, a group of law enforcement officers arrive at the room and there is another exchange of gunfire.

“You see the police officers actually getting blown back. One of them actually touches his head,” and suspects an injury, he said.

Over the next hour of the video, officers converge on the scene and gear up with helmets, assault rifles, ballistic shields, and tear gas canisters. But they do not take action.

“Essentially they stand there for an hour as these minutes tick by,” he said. “It’s not until 12:50 that we then see those police officers move to that classroom, breach the door, and take down the gunman.”

The reporter said the video intensifies questions about the response from local, state and federal agencies on scene.

“As to why it was handled the way it did and why the police did not move with a greater sense of urgency, I don’t think we’ve gotten to the truth of that yet,” he said.

“This video, once it is finally made public, is going to be very disturbing to many people and, I think, really deepen the tragedy that happened that day,” he said.

DPS director testifies for second time

The House committee began its latest hearing Monday morning. The witnesses scheduled to testify were McCraw, Uvalde County Sheriff Ruben Nolasco and John Curnutt, assistant director of the Advanced Law Enforcement Rapid Response Training Center.

On Thursday, Uvalde Mayor Don McLaughlin refuted a new assessment of the law enforcement response to the shooting, saying the report by the rapid response training center — an active shooter and attack response training provider at Texas State University — “does not give a complete and accurate account of what happened.”

McLaughlin took issue with the first part of the report, which said a Uvalde police officer with a rifle spotted the gunman outside the school, but a supervisor either did not hear the officer or responded too late when the officer asked for permission to fire.

“No Uvalde police department officer saw the shooter on May 24 prior to him entering the school,” McLaughlin said in a statement. “No Uvalde police officers had any opportunity to take a shot at the gunman.”

CNN has requested comment from Uvalde District Attorney Christina Mitchell Busbee on Friday and on Sunday about why she objects to the release of the video, but has not heard back.

According to the same source, the Texas House Investigative Committee’s preliminary report will clarify conflicting accounts from previous reviews of what happened on May 24. The report will include verbatim quotes from sworn testimony, the source said.

Nolasco told CNN on Sunday his testimony would be through video-conference, not in person.

Texas House Speaker Dade Phelan (R) created the three-member committee last month. Burrows, a Republican, was appointed chairman; Rep. Joe Moody (D) was appointed vice chair; and former Texas Supreme Court Justice Eva Guzman is a committee member.

The purpose of the investigative committee is a fact-finding one. Two other House committees, Youth Health & Safety and Homeland Security & Public Safety, will be tasked with making legislative recommendations.

Separately, Uvalde County Commissioners on Monday unanimously passed a resolution calling on Texas Gov. Greg Abbott to call a special session of the Texas Legislature to consider raising the minimum age of purchase for semi-automatic, assault style rifles from 18 to 21.

“Texans want to feel reassured that we can go to the grocery store, church, school, to the mall, and public events safely,” County Commissioner Roland Garza, who introduced the resolution, told CNN. “This might be a small step but something must be done. We want Governor Abbott to listen to us.”

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