The warrant portrayed Mr. Peterson, the only armed guard on campus, as an officer with a wealth of active shooter training who knew the gunman was inside, but did not go in to try to stop him as he killed and injured students and staff. It details a series of students and faculty who remembered seeing Mr. Peterson outside.

One student, Arman Borghei, told investigators that during the shooting, he looked out a third-floor window and saw Mr. Peterson standing on the side of the 1200 building “with his gun drawn not really doing anything.”

Since he was first interviewed by Broward detectives two days after the killings, Mr. Peterson has said he did respond, by alerting the police, locking the school down and evacuating children in the courtyard. “There wasn’t even time to think,” Mr. Peterson told The Washington Post. “It just happened and I started reacting.”

He said he has run the shooting over and over in his head. “It was my job, and I didn’t find him,” he said of the gunman.

Mr. Miller, who was the first supervisor on the scene, had told investigators that he heard three or four gunshots as he was arriving and believed they were coming from outside the school building. The investigation found that he had gone behind his car, outside of campus, and put on his bulletproof vest, and did not make his first radio transmission to direct a response until five minutes after he arrived — 10 minutes after the first radio communications about the shooting.

Meanwhile, four officers from the nearby Coral Springs Police Department arrived and entered the building where the shooting was occurring, the investigation showed.

In January, Florida’s newly elected Republican governor, Ron DeSantis, suspended the Broward County sheriff, Scott Israel, citing neglect of duty and “incompetence.” He named as his replacement Gregory Tony, a former sergeant with the Coral Springs Police Department. In his new position, Sheriff Tony oversaw an internal investigation of seven deputies at the department, including Mr. Peterson.