A trove of law enforcement documents and video obtained by The New York Times as part of an investigation into last months school shooting in Uvalde, Texas, shows police delayed entering the classroom in part because they feared for their own safety.

The school districts police chief, Pete Arredondo, arrived just two minutes after a gunman opened fire inside Robb Elementary School on May 24 after entering through an exterior door that failed to lock properly .

A group of officers approached the classroom the gunman was in soon after but then retreated after two Uvalde Police Department officers were grazed by bullets as they tried to peer through a window.

Despite the arrival of additional and better-armed officers, nobody attempted to approach the classroom again for more than 40 minutes, surveillance video reviewed by the Times showed.

In the meantime, children and teachers inside the room were in dire need of medical care, according to pleading, heart-rending phone calls from the students to 911. Its unclear if Arredondo was aware of the calls.

There is a lot of bodies, 10-year-old Khloe Torres told a 911 dispatcher , 37 minutes after the shooting began. I dont want to die, my teacher is dead, my teacher is dead, please send help, send help for my teacher, she is shot but still alive.

Torres survived, but 19 of her classmates and two of her teachers did not.

More than an hour later, a team of U.S. Border Patrol agents, equipped with the protective shields that Arredondo and the other officers lacked when they first entered the building, finally breached the classroom and killed the gunman, identified as 18-year-old Salvador Ramos, a former student.