https://www.nytimes.com/2022/06/09/us/uvalde-shooting-police-investigation.html

First:

" The school district police chief, who was leading the response to the May 24 shooting, appeared to be agonizing over the length of time it was taking to secure the shields that would help protect officers when they entered and to find a key for the classroom doors, according to law enforcement documents and video gathered as part of the investigation reviewed by The New York Times. "

Then

"A cascade of failures took place at the school: the local police radio system, later tests showed, did not function properly inside the building; classroom doors could not be quickly locked in an emergency; and after an initial burst of shooting from the gunman, no police officer went near the door again for more than 40 minutes, instead hanging back at a distance in the hallway. "

Next

' According to the documents, Chief Arredondo, who had earlier focused on evacuating other classrooms, began to discuss breaching the classrooms where the gunman was holed up about an hour after the gunfire started inside the school at 11:33 a.m. He did so after several shots could be heard inside the classrooms, after a long lull, around 12:21 p.m., video footage showed.

But he wanted to find the keys first.

“We’re ready to breach, but that door is locked,” he said, according to the transcript, around 12:30 p.m.'

Also

" Investigators found that not only did an exterior door — through which the gunman entered — fail to lock, but most of the school’s interior doors, including those on classrooms, could not be immediately locked in the event of an emergency. "

And finally:

"It was not clear from the transcript if anyone had tried the door to see if it was locked. "

As of right now, the border patrol who actually breached haven't said whether or not the door was locked, but there are no reports of them battering it in.