Washington — The Justice Department on Thursday has completed a blistering report on the response by law enforcement to the 2022 mass shooting in Uvalde, Texas, calling it a "failure."

Launched in late May 2022 at the behest of Uvalde Mayor Don McLaughlin soon after the shooting that took the lives of 19 children and two teachers, the "critical incident review" sought to provide an independent account of law enforcement responses and identify lessons to be learned and applied to future active shooter events. 

"The response to the May 24, 2022, mass casualty incident at Robb Elementary School was a failure," the 575-page report states.

The Justice Department found that 77 minutes elapsed from when law enforcement arrived on the scene to when the suspect was killed. Officers treated the situation not as an active shooter operation, but rather as a "barricaded suspect," the review found.

Citing a lack of urgency toward entering the classrooms at Robb Elementary School, the review found that many officers arriving on the scene incorrectly believed that the gunman had been killed, or that Pete Arredondo, the former police chief of the Uvalde Consolidated Independent School District, was in the room with the suspect.

Arrendondo, who was fired in the wake of allegations he made numerous critical errors during the shooting, receives much of the blame for the response.

Attorney General Merrick Garland is set to announce the findings during a news conference from Uvalde on Thursday. He met with the families of those killed in the shooting, and Justice Department officials privately briefed family members on the department's report on Wednesday night.

Video recorded during the shooting showed a delayed response by law enforcement on the scene. Authorities in Texas spent three days providing often conflicting and incomplete information about the 90 minutes that elapsed between the time the gunman entered the school and the moment when U.S. Border Patrol agents unlocked the classroom door and killed the shooter. Law enforcement officers from local, state and federal entities responded to the Uvalde shooting.

The Office of Community Oriented Policing, known as the COPS Office, carried out the Justice Department review. Similar reviews were conducted after mass shootings in San Bernardino, California, in 2015 and the Pulse Nightclub in Orlando in 2016. 

Nearly 20 officers were standing in the hallway outside the classrooms during the attack on Robb Elementary School for over 45 minutes before agents used a master key to open a door and confront the gunman, Texas Department of Public Safety Director Steven McCraw said at a news conference in May 2022.

The on-site commander "was convinced at the time that there was no more threat to the children and that the subject was barricaded and that they had time to organize" to get into the classroom, McCraw said.

"Of course it was not the right decision. It was the wrong decision," McCraw told reporters.

Jeff Pegues and Rob Legare contributed to this report.