Families of the children and teachers killed at Robb Elementary School sat in the courtroom this week as a former school police officer went on trial, seeking accountability nearly four years after the devastating mass shooting in Uvalde, Texas.

Among them were Jesse and Juanita Rizo, whose niece, Jackie Cazares, was one of the 19 children killed.

"We've been waiting four years for this day to come, and we want to see justice for our baby girl Jackie Cazares, the 18 children and the two teachers — the justice they deserve," Juanita Rizo said.

Adrian Gonzales, a former Uvalde schools officer, is facing state charges, accused of failing to act during the May 24, 2022, attack. He was the first officer on the scene and one of the first four officers to go inside the building.

As the gunman fired into classrooms full of children and teachers, however, prosecutors say Gonzales stayed where he was and did not move toward the gunfire.

Special prosecutor Bill Turner became emotional laying out Gonzales' alleged in action during opening statements to the jury on Tuesday, pointing out that others, including teachers, tried to protect children from the shooter.

"When a child is in danger and calls 911, we have the right to expect a response," Turner said.

An investigation found that 77 minutes passed from the time authorities arrived until the tactical team breached the classroom and killed the 18-year-old shooter, who was obsessed with violence and notoriety in the months leading up to the shooting.

Defense attorney Nico Lahood told the jury Gonzales was not in a position to see the shooter that morning, and was relaying information to other officers as they arrived.

"The government wants to make it seem like he just sat there. He didn't just sit there. He did what he could with what he knew at the time in what was a dynamic situation," Lahood said.

At the request of Gonzales' attorneys, the trial was moved to Corpus Christi after they argued Gonzales could not receive a fair trial in Uvalde.

The indictment accuses Gonzales of putting children in "imminent danger" of injury or death by failing to engage the shooter and by not following his training.  He faces 29 counts of child abandonment or endangerment. 

State and federal reviews of the shooting cited cascading problems in law enforcement training, communication, leadership and technology.