PARKLAND, Fla. (AP) — Ballistics experts will fire up to 139 shots at Marjory Stoneman Douglas High School on Friday during a reenactment of the 2018 Parkland massacre organized as part of a lawsuit that accuses a sheriff’s deputy of failing in his duty to protect the victims.

As the reenactment takes place, technicians outside a three-story classroom building will record the sound of the gunfire, seeking to capture what the deputy assigned to the school, Scot Peterson, heard during the six-minute attack.

The shooting, which sparked a nationwide movement for gun control, left 17 dead, 17 wounded and hundreds traumatized in the South Florida community. Former Stoneman Douglas student Nikolas Cruz, 24, pleaded guilty in 2021 and was sentenced to life in prison.

Peterson — who worked for the Broward Sheriff’s Office, also targeted in the lawsuit — says he didn’t hear all the shots and couldn’t pinpoint where they were coming from because of echoes. He got within feet of the building’s door and drew his gun, but then backed away and stood next to an adjoining building for 40 minutes, making radio calls. He has said he would have charged into the building if he knew that’s where the shooter was.

Families of the victims bringing the lawsuit contend Peterson knew Cruz’s location, but retreated out of cowardice and in violation of his duty to protect their loved ones.

Peterson, 60, was acquitted in June of felony child neglect and other criminal charges for failing to act, the first U.S. trial in history of a law enforcement officer for conduct during an on-campus shooting.

But the burden of proof is lower in a civil lawsuit. Circuit Judge Carol-Lisa Phillips allowed the test, but made clear she was not ruling on whether the recording will be played at trial. That, she said, will have to be argued later — it is likely Peterson’s attorneys will oppose the attempt. No trial date has been set. The families and wounded are seeking unspecified damages.

The experts will fire live ammunition from the same spots as Cruz, with an identical AR-15-style semiautomatic rifle. The bullets will be caught by a safety device. The school is closed for summer break and students and teachers are not on campus.

David Brill, the families’ attorney leading the reenactment, did not return calls and emails seeking comment. Peterson’s attorney, Michael Piper, declined comment.

Tony Montalto, president of Stand with Parkland, which represents most of the families, said while Peterson was acquitted of criminal charges “that doesn’t mean he’s not guilty of failing to do the right things.”

“He failed to properly react to the tragedy, he failed to enter the building and he failed to render aid. The reenactment is designed to disprove some of the statements that were made during the criminal trial,” Montalto said. His 14-year-old daughter, Gina, died in the shooting.

Peterson, who didn’t testify at his criminal trial, insisted he would have acted differently if he knew where the shooter was.

“Those were my kids in there,” Peterson said in a 2018 interview with NBC’s Today Show. “I never would have sat there and let my kids get slaughtered. Never.”

Robert Maher, a Montana State University professor who has studied the accuracy of gunfire recordings, said gunshots are much sharper in person.

“Speakers are not able to reproduce this high-intensity, short-duration pop sound,” Maher said.

Still, he said, there are techniques that might pick up the direction the shots were coming from and the reenactment should demonstrate how loud they were where Peterson was standing. That’s a significant question as the classroom building’s doors and window were mostly shut during the shooting.

“Are they really loud like you would expect a gunshot to be or, because the building is sealed up, not loud?” Maher said. “That’s probably what they are going to be able to get out of the reconstruction.”

Tamara Lave, a University of Miami law professor, said when Judge Phillips decides whether to allow the jury to view and hear the reenactment, she will consider whether it “fairly and accurately” depicts what Peterson heard — but it doesn’t have to be perfect.

“It has got to be close enough to be fair and help the jury determine whether he actually heard the shots,” Lave said.

Parkland sent warnings to residents so they won’t panic if they hear the gunshots and to help them prepare mentally. Eagles’ Haven, a community wellness center opened after the shooting, is planning several programs Friday including yoga, tai chi, a drum circle and meditation along with food so people can talk.

“When you are feeling triggered, it is good to be with other people who understand what you are going through,” said Sarah Franco, the center’s director.

University of California, Santa Barbara Professor Erika Felix, who studies community trauma after mass shootings, agreed. She said the reenactment “will bring up thoughts, feelings, emotions. It’ll bring up memories.”

Before Friday’s reenactment, two South Florida congressmen, Democrat Jared Moskowitz and Republican Mario Diaz-Balart, will lead several colleagues from the School Safety and Security Caucus on a tour of the building, which has remained mostly untouched since shortly after the shooting. Floors are still covered with dried blood, books and computers remain on desks and classrooms contain wilted Valentine’s Day flowers and deflated balloons.

They will then meet with family members and survivors. Moskowitz is a Stoneman Douglas graduate.

After Friday, the Broward school district says it will begin demolishing the building. It had remained standing as evidence in the Cruz and Peterson criminal trials, looming over the campus behind a chain-link fence.