Chief Pustizzi called it a communications failure. The video system allows for real-time playback.

“At first the guys are hearing, ‘Oh, he’s on the second floor.’ Well, it’s not true, ’cause we have people on the second floor and the people are saying, ‘Well, he’s not on the second floor,’ ” Chief Pustizzi said, adding that, if anything, the officers were “more expeditious” as they moved through the school under the belief the gunman was still there.

Coral Springs police have said they were the first to respond to the shooting. Sheriff Israel, who defended his office’s response on Wednesday and said his own deputies had not hung back outside the building, said on Thursday that the Coral Springs officers acted “heroically.”

Samantha Fuentes, an 18-year-old senior at Stoneman Douglas High who was shot in both legs, said she never saw Deputy Peterson during the “30 minutes” that passed before SWAT officers arrived at the first-floor classroom in which she and other students had been taking a class.

“He is not someone who has much of a presence” in the school, she said.

Sheriff Israel, flanked by two of his top aides, appeared emotional Thursday during the news conference in which he described Deputy Peterson’s conduct. His eyes appeared to glisten, and his speech was sometimes halting.

The two other deputies placed on restricted duty pending an internal investigation were identified by the sheriff’s office as Edward Eason and Guntis Treijs.

In November 2017, a caller told the authorities that Mr. Cruz had been stockpiling guns and knives. In a summary of the call, the sheriff’s office said the caller, located in Massachusetts, worried that Mr. Cruz “will kill himself one day and believes he could be a school shooter in the making.” A deputy contacted the person who called, but no report was filed. The caller was referred to the sheriff’s office in Palm Beach County, where the caller said Mr. Cruz lived.

In February 2016, the sheriff’s office received what it described as “thirdhand information” that Mr. Cruz “planned to shoot up the school” and had posted a picture on Instagram of a “juvenile with guns.” A deputy determined that Mr. Cruz had knives and a BB gun and forwarded the information to the school resource officer at Stoneman Douglas High. That was Deputy Peterson.