The classroom door in the Uvalde primary school where 19 children and two teachers were killed last month was not locked, even as police waited for a key, the Texas Department of Public Safety Director has said.
There was no evidence that any law enforcement officer ever tried the classroom door to see if it was locked, Steven McCraw said at a Texas Senate hearing into the shooting.
"I don't believe based on the information we have right now that door was ever secured," Mr McCraw said.
"He (the shooter) didn't have a key ... and he couldn't lock it from the inside."
Mr McCraw said that evidence shows the law enforcement response to the shooting was "an abject failure".
"There is compelling evidence that the law enforcement response to the attack at Robb Elementary was an abject failure and antithetical to everything we've learned," he said.
Police actions after the gunman entered the primary school and began shooting have come under close scrutiny amid anguished parents' anger over the response.
"Three minutes after the subject entered the west building, there was a sufficient number of armed officers wearing body armour to isolate, distract and neutralise the subject," Mr McCraw added.
"The only thing stopping a hallway of dedicated officers from entering Room 111, and 112, was the on-scene commander, who decided to place the lives of officers before the lives of children," the director said in the hearing.
Uvalde schools police chief Pete Arredondo said earlier this month he never considered himself the incident commander of the scene of the shooting, and that he did not order police to hold back on breaching the building.
Community members along with parents of the victims urged Mr Arredondo to resign during an impassioned school board meeting on Monday night, ABC News reported.
Earlier this month, the great-grandfather of one of the young victims berated police near the memorial of white crosses surrounded by wreaths and bouquets of flowers.
"They could tell me 'Oh, we made a mistake. We made the wrong decision'. But my great-granddaughter is not coming back to me," said a distraught 78-year-old Ruben Mata Montemayor.
Meanwhile, US Senator John Cornyn, the lead Republican negotiator in bipartisan gun legislation talks, has said that negotiators expected to introduce a bill to address mass shootings.
The Texas Republican said negotiators, including his fellow Republican Senator Thom Tillis and Democratic Senators Chris Murphy and Kyrsten Sinema, spoke early in the day by phone and were now waiting for staff to produce legislative text.
"I think we're on a glide path, and hopefully it will land shortly," Mr Cornyn said in an interview shortly after speaking with his fellow negotiators. He added that he expected the bill to be introduced on the Senate floor later in the day but gave no specific time.
Introducing the bill would improve the odds of Senate passage before politicians leave for their two-week July 4 break at the end of this week.
The bipartisan group has been working on a deal to curb gun violence since the primary school shooting in Uvalde, Texas, less than two weeks after a shooting at a supermarket in Buffalo, New York, left ten dead.
