The Parkland, Florida, high school massacre will be reenacted in the same building on Friday as a part of a lawsuit against former school officer Scot Peterson, who is accused of retreating while students were being shot.

As ballistics experts fire shots with a weapon identical to the AR-15-style semi-automatic rifle used in the mass shooting, specialists outside the building will record the sound to try to prove what Peterson heard or didn't hear during the massacre, according to The Associated Press.

Peterson has said he couldn't decipher where the gunfire was coming from because of echoes.

Seventeen students and staff were killed in the Feb. 14, 2018, mass shooting at Marjory Stoneman Douglas High School. Since then, the 1200 building has sat untouched like a time capsule, with dried blood on furniture and students' strewn papers on the floor.

Last month, victims' families were permitted to go inside the building for the first time, since the criminal trials had concluded for Peterson, who was acquitted on all charges including child neglect, and gunman Nikolas Cruz, who was convicted and sentenced to life in prison.

Max Schachter, whose 14-year-old son, Alex, was among the 17 killed, told ABC News that Alex's classroom looked "like a horror scene from a war zone."

"It was grotesque," he said. "There was so much blood everywhere, especially around Alex's desk."

But Schachter needed to be there, he said, because "that was the last place he took his last breath."

Schachter was among the families who returned to the building on Friday morning to tour the site with several members of Congress ahead of the ballistics reenactment.

While some families want the 1200 building torn down, Schachter said he wants it to remain until every legislator walks through. As difficult as it is to face the harrowing site, politicians must "understand the failures before and during the shooting" to "hopefully ensure safer schools tomorrow," he tweeted.

Families are seeking unspecified damages in the lawsuit against Peterson and the Broward Sheriff’s Office, according to the AP.