Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

FORT LAUDERDALE, Fla. — The first deputy on the scene of the deadly shooting at a Florida high school last month disregarded his training by failing to enter the school and confront the gunman, a senior sheriff's official said Thursday.

The officer, former Broward County sheriff's Deputy Scot Peterson, alerted dispatchers to the shooting at Marjory Stoneman Douglas High School in Parkland on Feb. 14 within two minutes of its being reported to 911, according to audio dispatches released by the sheriff's office on Thursday.

But instead of rushing into the school, where he was assigned as a resource officer, Peterson remained outside and began radioing orders for fellow deputies to seal off the roads and intersections around the campus.

Eleven minutes elapsed before sheriff's deputies and Coral Springs police officers finally entered the building, the dispatch audio indicates. By then, the suspected gunman, 19-year-old Nikolas Cruz, had already fled the scene.

On Friday, an additional 17 charges of attempted murder were officially filed against Cruz — adding to the 17 counts of first-degree murder he was already facing. The new counts represented each of the survivors injured during the rampage.

Cruz, dressed in an orange prison jumpsuit, kept his head bowed during the one-minute hearing, in which Broward Judge Kim Theresa Molica in Fort Lauderdale again denied his bond request. He is due back in court next week for his arraignment.

A circuit grand jury had formally indicted the alleged gunman on 34 counts earlier in the week. Cruz initially pleaded not guilty last month, but he withdrew the plea on Thursday to "stand mute" to the charges.

Related: Fight, flight or freeze? Officers rarely fail to confront threat, experts say

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

As the case moved through the court, criticism over the police handling of the crisis was far less muted. Col. Jack Dale, head of the department's criminal investigations and internal affairs units, said Thursday that the audio police dispatches make it clear that Peterson had disregarded the training deputies undergo for such situations.

"First, interrupt the shooter, and that is the primary mission of an active shooter response," Dale said in an interview with NBC Miami. "When an active shooter ceases, then those secondary responses become appropriate."

Complicating the initial response was that Broward sheriff's deputies and Coral Springs police use different radio channels, so "anything that occurred on the Coral Springs channel would not be able to heard by the deputies on the scene and vice versa,” Dale said.

Still, he said, "I don't know that any chaotic scene like this ever goes perfectly."

Peterson, 54 — whom President Donald Trump called a "coward" last month — was suspended without pay and soon resigned, the sheriff's office said a week after the shooting.

His attorney said at the time that Peterson "is confident that his actions on that day were appropriate under the circumstances" and that all of the evidence, taken as a whole, "will exonerate him of any sub-par performance."

Transcripts of 911 calls released by the Broward County Sheriff's Office reveal the tense and agonizing moments of students being trapped inside the school and parents scrambling for more information.

"Shots at Stoneman Douglas, someone's shooting up the school," an unidentified student reported in an emergency call that cut off after less than 40 seconds.

In another call, a mother was on another phone with her daughter, who was huddled with fellow students in a barricaded classroom.

"Stay together, I love you, I love you ... Lord God, Lord God, it's OK," the mom said.

"Can you hide somewhere?" she added. "Can you play dead? ... If he shoots, you need to play dead."

Cruz's public defenders said in a court filing that his earlier plea was filed "prematurely" and that "having now been indicted by the Grand Jury, the Defendant Nikolas Cruz withdraws that filing and Stands Mute to the Charges."

Standing mute is different from pleading nolo contendere, or "no contest," which courts treat as the equivalent of a guilty plea.

Standard procedure when a defendant stands mute is for the judge to enter a not guilty plea on the defendant's behalf — allowing the defendant to enter no plea while reserving the right to contest the charges later at a trial.

The Broward County Public Defender's Office last month said Cruz would plead guilty and spare families the pain of a trial if prosecutors promise not to pursue the death penalty.

Matthew Vann reported from Fort Lauderdale, and Alex Johnson reported from Los Angeles. Ethan Sacks contributed reporting from New York.