A grand jury in Uvalde, Texas, has indicted former school district police chief Pedro Arredondo over the police response to the 2022 shooting at Robb Elementary School in which 19 students and two teachers were killed.
The Uvalde County Sheriff's office said Mr Arredondo was in custody and was being booked on ten counts of child endangerment.
Officers left the 18-year-old gunman alone inside a classroom with children for more than an hour while weighing how to confront him. By the time officers stormed in, the school had become the scene of one of the deadliest shootings in US history.
Another law enforcement officer, Adrian Gonzales, was also indicted by the grand jury, according to local media reports. The sheriff's department said Mr Gonzales had not yet been booked and said they could provide no details on his situation.
The charges against Mr Arredondo and Mr Gonzales are the first criminal complaints lodged against any responding officers.
Uvalde County District Attorney Christina Mitchell confirmed to the Uvalde Leader-News newspaper that both Mr Arredondo and Mr Gonzales were indicted. She told the paper that more details would be provided once Mr Gonzales is booked, which she said would take place today.
Federal and state investigations into the school shooting condemned the responding officers' inaction.
In May, the families of the victims filed lawsuits against Meta, Activision Blizzard and its parent Microsoft, along with gunmaker Daniel Defense, for what they claim was collusion in marketing weapons to young people.
In an advisory earlier this week declaring gun violence in the country a public health crisis, the US surgeon general noted it has been the leading cause of death among children and adolescents in the country since 2020.
He also noted that the firearm mortality rate among youths in the US is 11 times higher than in France, 36 times higher than in Germany and 121 times higher than in Japan.
