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. 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. 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. 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. Texas investigators say Arredondo mistakenly treated the shooting as a barricaded suspect incident instead of an active shooter situation.