uvalde police cops
© AP Photo/Dario Lopez-MillsPolice waited 77 minutes to attempt entering Robb Elementary, a new report said.
Security footage shows cops at the Uvalde, Texas school massacre waited 77 minutes before even trying to open the doors to two classrooms where the shooter killed 19 children and two teachers last month, a new report said.

The latest revelation, published Saturday by The San Antonio Express News, is the latest detail that shows a botched police response to the massacre, which is now under investigation by the Texas Department of Public Safety.

Video shows that gunman Salvador Ramos, 18, was able to open the door to classroom 111 on May 24, even though it was supposed to lock automatically when shut and only be opened from the outside with a key, the newspaper said.

Once inside the classroom, Ramos was able to access classroom 112 through another interior door.

It was unclear if the door was locked while Ramos conducted the shooting spree, but police did not even check or try to open it, despite having access to a Halligan tool which could have broken the lock, according to the report.

Uvalde school district police Chief Pete Arredondo was in charge of the operation. He previously told The Texas Tribune that he waited for 40 minutes for keys from the custodian to try to open the classroom door.

Footage now shows that when Arredondo eventually got the key ring, he was trying to open other doors to find a master key, not the doors to classroom 111 and 112, according to the Express News.

"Each time I tried a key I was just praying," Arredondo told the Texas Tribune. "The only thing that was important to me at this time was to save as many teachers and children as possible."

He tried dozens of keys, but told officers to wait for a tactical team when none worked, the report said.

Finally, at 12:50 p.m., police breached the door and shot and killed the suspect who had first broken into the school at 11:33 a.m. through an exterior door that had also failed to automatically lock.

During that excruciating and deadly 77-minute span, seven desperate 911 calls were made by students and teachers inside the classrooms under fire as the carnage piled up.

Texas investigators say Arredondo mistakenly treated the shooting as a barricaded suspect incident instead of an active shooter situation, where the top priority is for cops to confront the suspect to stop the violence.