By Brad Brooks and Nathan Layne

July 17 (Reuters) - A Texas legislators' probe of the Uvalde school shooting that left 21 dead blamed "systemic failures" and poor leadership for contributing to the death toll, a report released on Sunday found.

The Texas House of Representatives committee investigation marked the most exhaustive attempt so far to determine why it took more than an hour for police and other officers to confront and kill the 18-year-old gunman at Robb Elementary School on May 24.

The bottom line, the report found, is that "law enforcement responders failed to adhere to their active shooter training, and they failed to prioritize saving the lives of innocent victims over their own safety."

The 77-page report said 376 law enforcement officers rushed to the school in a chaotic scene marked by a lack of clear leadership and sufficient urgency.

"Other than the attacker, the Committee did not find any 'villains' in the course of its investigation," the report stated.

"Instead, we found systemic failures and egregious poor decision making."

"The void of leadership could have contributed to the loss of life as injured victims waited over an hour for help, and the attacker continued to sporadically fire his weapon."

Uvalde Mayor Don McLaughlin said in an emailed statement that the city had placed Lieutenant Mariano Pargas, who was the acting city policy chief on the day of the shooting, on administrative leave.

Pargas did not immediately respond to a request for comment from Reuters.

State police officials have sharply criticized the leadership of Pete Arredondo, the police chief of the school district's six-man police force, who state police have said was in control of the scene.

But the report noted that hundreds of officers from agencies that were better trained and better equipped than the school police force badly failed, too.

"Despite an obvious atmosphere of chaos, the ranking officers of other responding agencies did not approach(Arredondo) or anyone else perceived to be in command to point out the lack of and need for a command post, or to offer that specific assistance," the report stated.

The mayor McLaughlin also on Sunday released body camera footage from some of the city police officers who responded to the shooting, which showed the confusion of the scene.

The body cam footage of one officer who was among the first to arrive inside the school, just a few minutes after the gunman had fired over 100 rounds inside the classrooms, showed the chaos.

The officer approached the door of the classroom and was grazed with one of the gunman's shots.

He asked fellow officers in the hallway if he was bleeding, then momentarily retreated outside the school.

"He's in the class!," the officer told colleagues outside. "We gotta get in there! We gotta get in there, he just keeps shooting!"

SHORTCOMINGS AND FAILURES

The report found multiple failures at the school, noting the five-foot tall exterior fence around the school that could not impede the gunman. There was also a "regrettable culture of noncompliance by school personnel" when it came to leaving exterior and interior doors unlocked or propped open. The gunman easily entered the school through an unlocked door.

The report also found that of the approximately 142 rounds the attacker fired inside the building, it was "almost certain" that around 100 of those shots were fired before any officer entered the school.

The report described "shortcomings and failures of the Uvalde Consolidated Independent School District and of various agencies and officers of law enforcement" and "an overall lackadaisical approach" by the authorities.

Part of that could be explained by communications failures.

Children inside the classrooms where the killing took place called 911 and pleaded for help, but the report said that nobody ensured that responders making key decisions inside the building knew about those emergency calls or "received information that students and teachers had survived the initial burst of gunfire."

"Nobody in command analyzed this information to recognize that the attacker was preventing critically injured victims from obtaining medical care," the report stated.

CALLS FOR ACCOUNTABILITY

The report also found there was a "relaxed vigilance" on the school campus because of the frequency security alerts were issued that resulted from nearby police confrontations with human traffickers carrying illegal immigrants.

Video posted last week by the Austin American-Statesman newspaper showed police took cover in a hallway for 77 minutes before they stormed the two joined classrooms and exchanged fire with the gunman.

Authorities said in May that frantic children inside the classrooms called 911 at least six times while officers waited in the hallway.

Representative Dustin Burrows, a Republican who headed the committee, said at a Sunday news conference that the goal of the investigation was to provide a basis of facts so that lawmakers could make future policy changes to make schools more secure.

Burrows said the scope of the lawmakers' investigation did not drill down into exactly what individual officers on the scene knew and when - that would have to be left to the individual agencies to discover.

"If somebody failed to exercise their training, if somebody knew there were victims in there being killed or dying and did not do more, I believe those agencies will have to find accountability for those officers," Burrows said.

Joe Moody, a Democratic lawmaker who was part of the investigative committee, said that mass failures of law enforcement in Uvalde was a painful reality.

"It's hard to hear that there were multiple systemic failures because we want to tell ourselves that systems work ... we want to tell ourselves that this won't happen again. That's just not true," Moody said.

(Reporting by Brad Brooks in Lubbock, Texas, and Nathan Layne in Wilton, Connecticut; Additional reporting by Tyler Clifford in New York and Diane Bartz in Washington; Editing by Diane Craft, Daniel Wallis and Stephen Coates)