The elite tactical agents in the Border Patrol credited with taking down the gunman in Tuesday’s mass shooting at Robb Elementary School in Uvalde, Texas, thought they were attempting a “suicide” mission in charging a barricaded shooter, a senior Homeland Security official said.

Parents on the scene outside the school amid the chaos criticized law enforcement for taking too long to act. A senior federal law enforcement official familiar with the investigation into the incident told the Washington Examiner on Thursday that the Border Patrol agents had been appointed by the local and state law enforcement on the site to lead that aspect of the response.

First responders on the scene recognized that the attacker, Salvador Ramos, had barricaded himself inside a classroom and was not targeting other classrooms. The early reporting on the shooting included confusion about whether Ramos targeted one or two classrooms.

“It was two rooms that were connected, so that’s why there’s misinformation. The gunman went into both,” the federal official said. “By entering the door from the hallway, you’d have access to both.”

Ramos had barricaded himself inside the joint classroom with his Ar-style semi-automatic rifle, a weapon superior to the handguns police were carrying. The official said that breaching the room was seen as nearly impossible because of the disparity.

“If you have a barricaded subject and he has the advantage because he’s barricaded — if you rush through the door, not only do you have dead kids but dead cops,” the official said. “It’s suicide to try to rush a barricaded subject.”

Police wanted to keep Ramos in an isolated area to prevent him from going to other classrooms.

Because of the school’s location in a town of 15,000 residents located just 60 miles from the U.s.-mexico border and itself the home to a Border Patrol station, federal agents were among the police who responded to the shooting. While some police broke windows in order to pull children and teachers from the unaffected classrooms, highly trained agents who came in from the surrounding area were tasked with coming up with a plan to confront the attacker.