PARKLAND, Fla. (AP) — A police officer who rushed into a high school building during the 2018 Parkland shooting testified Friday that a sheriff's deputy outside confirmed that the shooter was upstairs.

The former Broward County deputy, Scot Peterson, is on trial for failing to confront the shooter who killed 17 people at Marjory Stoneman Douglas High. He has insisted since he spoke to investigators two days after the massacre that he couldn’t tell where the gunshots were coming from, and that he thought they may have been fired outside.

On the third day of Peterson's trial, Coral Springs officer Richard Best related what he says Peterson told him outside the classroom building, WPLG-TV reported.

“I said, ‘Hey brother, what do we got?’” Best told the jury. “He said, ‘Gunshots second or third floor.’”

Peterson, 60, could be sentenced to nearly a century in prison if convicted.

“It is understood that the longer you wait, the more damage is being done,” Best said. “Every time you heard a gunshot, somebody might be dead.”

Peterson is charged with failing to confront shooter Nikolas Cruz before the gunman reached the building’s third floor, where he killed six people. The deputy is not charged in connection with the 11 deaths on the first floor, before he reached the building.

Peterson arrived at the building with his gun drawn 73 seconds before Cruz reached the third floor. Peterson took cover 75 feet (23 meters) away in the alcove of a neighboring building, his gun drawn. He didn’t leave his spot for about 40 minutes — around 35 minutes after the shooting had stopped.

Arman Borghei, who was a student on the building's third floor during the shootings, said he looked out of a window and spotted Peterson below with his gun drawn.

Borghei said he was "really scared, wondering when help would arrive,” but never saw Peterson approach the building.

Best testified that he considered it his job to risk his life to stop a threat and render aid.

“It is not that as one police officer I want to go inside by myself,” Best said. "But that is our training — to go inside.”

The most serious charges against Peterson are seven counts of felony child neglect.

For Peterson to be convicted of child neglect, prosecutors must first show he was legally a caregiver to the juvenile students — defined by Florida law as “a parent, adult household member or other person responsible for a child’s welfare.”

If jurors find Peterson was a caregiver, they must determine whether he made a “reasonable effort” to protect the children or failed to provide necessary care.

Peterson is the first U.S. law enforcement officer ever charged for an alleged failure to act during a school shooting. Similarly, Texas authorities are investigating officers in the town of Uvalde who didn’t confront the shooter who killed 19 elementary students and two teachers last year. None have been charged, however.

The trial began Wednesday and is expected to last up to two months.

Cruz, 24, pleaded guilty and last year received a life sentence.