The guns and ammunition weren't real, but like in the real world, officers and deputies were called in, learning the details as they unfolded.
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Two dozen officers and deputies participated in the three-day course.
Santa Ana Police Department Major Enforcement Team Commander Oscar Lizardi was one of the training instructors.
"The expectations and the goals are that they not only understand the tactics, they understand the training that they're receiving, but most importantly, the decisions that need to be made as a first responder to an event like this," Lizardi said.
Those decisions must come quickly and are under increased scrutiny as more witnesses record first responders on the job.
The videos document their actions and are often shared on social media.
Several recordings show onlookers outside Robb Elementary School in Uvalde, Texas, on May 24, the day 19 students and two teachers were shot and killed.
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Parents are heard pleading with officers to make entry, but investigators say after arriving on scene, more than an hour passed before officers breached the door ending the standoff with the gunman.
Several agencies, including the Texas Department of Public Safety, are investigating the response by law enforcement.
The Santa Ana Police Department said this type of preparation is unique to these situations and participants are learning to act without hesitation to save lives.
"We do not expect them to respond this way at any other call for service other than to save somebody's life or prevent some great bodily injury or death from occurring," Lizardi said. "That being said, the expectation is that they don't hesitate. We've been saying that now for years. We learned that from the Columbine incident."
According to the SAPD, 3,000 first responders total from throughout Orange County have participated in the training over the last 11 years.