A teacher who was wounded in the Uvalde mass shooting at Robb Elementary school is speaking out about his traumatic experience. All 11 students in his classroom were killed.

Arnulfo Reyes, a fourth-grade teacher at the school, tells Good Morning America that his class was watching a movie around 11:30 a.m. on May 24 when they heard gunshots. He instructed the kids to get under a table like they were trained to, and told them to “act like you’re asleep.”

Reyes says when he turned around, the gunman was already standing in his classroom and shot him multiple times. He said he also played dead after sustaining his injuries, and remained that way during the approximately 80 minutes the shooting continued.

“I told myself, I told my kids to act like they’re asleep, so I’m going to act like I’m asleep also,” he said of an ordeal that would last roughly 80 minutes. “And I prayed and prayed that I would not hear none of my students talk.”

The gunman killed every single student in Reyes' classroom and eight more students in a neighboring classroom.

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According to Reyes, before the gunman entered the room, one of the students called out to a police officer for help after hearing them enter the school, but the police had already retreated from the grounds—despite the fact that there was still an active shooter inside the school.

"One of the students from the next-door classroom was saying, 'Officer, we're in here, we're in here,'" he said. "But they had already left."

Uvalde police arrived at the school within minutes of the shooting, but waiting about an hour before actually confronting the gunman. The police department has come under fire in the days after the shooting. According to the New York Times, Chief Arrendondo of the Uvalde police department didn't have a radio on him during the shooting, which likely impeded his ability to communicate with police dispatchers. Two supervisors from the department were grazed by bullets fired by the gunman, which led the chief to decide to fall back.

Police fell back for more than an hour. Examinations of the police response found communication breakdowns, lapses in judgment, and tactical decisions were all out of line with years of police preparations for school shootings. These misdeeds may have contributed to additional deaths, and also delayed critical medical attention to those who were wounded during the shooting.

The Texas Department of Public Safety reports that several officers entered the school building shortly after the gunman did, but they were met with gunfire and retreated. The school police chief made “the wrong decision” to fall back instead of confronting the shooter, the public safety director says, even though more than a dozen officers stood outside the classroom while the murders continued.

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Understandably, Reyes has strong feelings about the Uvalde police response.

"After everything, I get more angry because you have a bulletproof vest. I had nothing," Reyes says. "You're supposed to protect and serve—there is no excuse for their actions, and I will never forgive them."

He tells GMA that he regrets not being able to do more for his students.

“We set them up to be like ducks,” he said.

As for the parents of each of his students, Reyes has a message for them: “I’m sorry. I tried my best. Please don’t be angry with me.”