A Justice Department investigation released on Thursday found that a near-total breakdown in policing protocols hindered the response to the 2022 school shooting in Uvalde, Texas, that left 21 people dead — but the gravest error was the reluctance of officials to confront the killer during the first few minutes of the attack.

The department blamed “cascading failures of leadership, decision-making, tactics, policy and training” for the delayed and passive law enforcement response that allowed an 18-year-old gunman with a semiautomatic rifle to remain inside a pair of connected fourth grade classrooms at Robb Elementary School for 77 minutes before he was confronted and killed.

The “most significant failure,” investigators concluded, was the fateful decision by local police officials to classify the incident as a barricaded standoff rather than an “active-shooter” scenario, which would have demanded instant and aggressive action regardless of the danger to those responding or the lack of appropriate weapons to confront the gunman.