There will be an investigation into law enforcement's response to the massacre at Robb Elementary School in Uvalde, Texas, which claimed the lives of 19 students and two teachers, the U.S. Justice Department announced on Sunday.

DOJ spokesman Anthony Coley stated in a statement, "At the request of Uvalde Mayor Don McLaughlin, the U.S. Department of Justice will conduct a Critical Incident Review of the law enforcement response to the May 24 mass shooting in Uvalde, Texas."

As Texas authorities and law enforcement have been under increasing criticism for how officers responded to the shooting, the review is a significant milestone.

The killing, the bloodiest school shooting in the United States since the 2012 Sandy Hook incident, has been followed by contradictory government versions of how it transpired.

The prolonged police standoff with the mass shooter has infuriated parents, with some claiming that a speedier response could have saved children's lives.

CNN has stated that police in Uvalde did not follow the active shooter procedure created following the Columbine school shooting in 1999, which instructs officers to stop the shooter as quickly as possible and even to forego aiding the injured.

CNN claimed that while the gunman was inside neighboring classrooms, 19 law enforcement officers waited outside the classroom for around 50 minutes for room keys and tactical equipment.

Governor Greg Abbott of Texas stated on Friday that he is requesting a complete explanation of what transpired during the school shooting, claiming that he was first "misled" by law enforcement officers conducting the investigation into the attack.

At a news conference in Uvalde, the Republican governor stated, "My expectation is that the law enforcement leaders who are directing the investigations will uncover every detail with full confidence."

The Justice Department inquiry aims to give an unbiased account of law enforcement activities and responses that day, as well as identify lessons learned and best practices to assist first responders in preparing for and responding to active shooter events, DOJ spokesman Conley said.

The Department's Office of Community Oriented Policing will conduct the review, he continued. "As with previous Justice Department assessments of mass shootings and other major incidents, this evaluation will be fair, public, and impartial," he added.

At the conclusion of its investigation, the Justice Department will issue a report with its findings.