Corpus Christi, Texas - A jury on Wednesday acquitted an ex-cop for his response to the 2022 Uvalde school shooting which killed 21 people, to the frustration of the victims' families.

Adrian Gonzales was accused of failing to "engage, distract or delay the shooter," and faced 29 felony counts of child endangerment – one for each of the 19 children who died and the 10 who survived. The jury took several hours to deliberate.

"In each of the 29 counts, we the jury find the defendant, Adrian Gonzales, not guilty," Judge Sid Harle said as he read the verdict at the end of the trial in Corpus Christi.

Nineteen young children and two teachers were killed in Uvalde on May 24, 2022 when a teenage gunman went on a rampage with an AR-15 style assault rifle at Robb Elementary School, in what was deadliest US school shooting in a decade.

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The official response by law enforcement was heavily criticized after it emerged that more than a dozen officers waited for over an hour outside classrooms where the shooting was taking place and did nothing as children lay dead or dying inside.

Family members voiced frustration at the decision, which followed an uncommon attempt to hold law enforcement accountable for their response to a mass shooting.

"They failed the children again," Javier Cazares, the father of Jackie Cazares who was killed in the attack, told press. "I've been emotionally shattered since day one, but again, we had to brace for the worst."

A total of 376 officers – border guards, state police, city police, local sheriff departments and elite forces – responded to the massacre, a Texas state lawmakers' report said in July 2022, yet they failed to stop it.

The shooter, identified as 18-year-old Salvador Ramos, was killed at the site of the attack.

Former school district police chief Pete Arredondo also faces charges over the tragedy, but will be tried separately and has pleaded not guilty to the charges he faces.