Victims' families have expressed their outrage after a report cleared police of wrongdoing over the deadly 2022 mass school shooting in Uvalde, Texas.
Independent investigator Jesse Prado said the police officers had acted in good faith - contrary to earlier findings criticising the slow response.
"You call that good faith? They stood there 77 minutes," said Veronica Mata, whose 10-year-old daughter was killed.
Gunman Salvador Ramos, an ex-student, killed 19 pupils and two teachers.
The 24 May, 2022 attack was one of the deadliest school shootings in US history.
Mr Prado's presentation triggered a furious response by some of the victims' families.
Several family members of those killed in the shooting walked out in anger before Mr Prado finished his presentation at Uvalde's city hall.
Parents' unimaginable grief a year after US massacre
The former police detective, tasked by Uvalde' city council with investigating the local police response to the shooting at Robb Elementary School, presented his findings on Thursday.
He said the police had committed no serious acts of misconduct.
At the same time, the investigator said there were communication problems between the responding officers, poor training for live shooter situations, lack of specialist equipment and delays in breaching the classroom where the gunman was.
Ms Mata was quoted by CNN as saying police had "waited after they got call after call that kids were still alive in there" before going in.
"We're going to stand here and we're going to keep fighting for our own, because nobody else is going to do it," she added.
Previous scathing reports by multiple US federal agencies have faulted the Uvalde Police Department officers at virtually every level.
In January, the US justice department said in its sharply critical report that chaos and a lack of urgency had plagued the police response.
The report described how police officers remained in a hallway or outside the school as the gunman shot dozens of people in two classrooms.
Nearly 400 officers responded to the attack - but it took 77 minutes after the first officers arrived for police to confront and kill the 18-year-old shooter, according to the document.
That slow response was the major focus of the report, which found police had failed to understand there was an active shooter and said there were "cascading failures of leadership, decision-making, tactics, policy and training".
