Jurors are due to begin a third day of deliberations Wednesday to mull a verdict in the trial of the former school resource officer who stayed outside during the 2018 massacre at a Parkland, Florida, high school in a rare trial focused on law enforcement response to a mass shooting.

State prosecutors accuse Scot Peterson, 60, of ignoring his training and doing nothing as 17 people, including 14 students, were gunned down at Marjory Stoneman Douglas High School -- the deadliest high school shooting in US history. His attorney argued the then-deputy for the Broward Sheriff's Office didn't enter the building because he couldn't tell where the shots were coming from.

Peterson has pleaded not guilty to 11 counts, including seven felony counts of child neglect and three misdemeanor counts of culpable negligence. He also faces a misdemeanor count of perjury for allegedly lying to investigators about the number of gunshots he heard after arriving at the scene.

Jurors are deliberating as Americans continue to grapple with mass and school shootings, with about 200 attacks on K-12 campuses since the Valentine's Day carnage at the Parkland school, according to a CNN tally. Some 332 shootings with at least four wounded, not including a shooter, have been recorded so far this year, the Gun Violence Archive reports.

The Parkland shooter is serving life in prison without parole after pleading guilty to 17 counts each of murder and attempted murder.

Origin of gunshots among trial issues

Peterson is accused of failing to confront the gunman according to his active shooter training, instead taking cover for more than 45 minutes outside the school's three-story 1200 building before the gunman was apprehended.

Peterson "left behind an unrestricted killer to spend the next 4 minutes and 15 seconds wandering the halls at his leisure," Assistant State Attorney Kristen Gomes said. "Because when Scot Peterson ran, he left children trapped inside of the building with a predator unchecked."

The charges against Peterson reflect the deaths and injuries of seven students and three school employees on the third floor of the 1200 building. Peterson was not charged in connection with the victims on the first floor because he had not yet arrived on scene. No one was killed on the second floor.

Peterson, who retired as criticism of his alleged failure grew, never knew where the shooter was, defense attorney Mark Eiglarsh told jurors, pointing to other witnesses who testified they could not narrow down where the deadly shots originated. The trial included testimony from former students, staff and members of law enforcement who supported the ex-deputy's claim it was difficult to hear where the gunfire was coming from.

"Two dozen witnesses came in here one by one and told you they couldn't tell from the sounds precisely what area we're talking about," Eiglarsh said in his closing argument Monday. And even if Peterson had known where the shooter was, speculation he could have made a difference is false, Eiglarsh argued.

Jurors also heard from witnesses who testified they knew the shots were emanating from the 1200 building, as well as law enforcement officers who testified their training dictated they move toward the sound of gunfire to confront a possible shooter.

Eiglarsh has emphasized Peterson was at the scene for the last 4 minutes and 15 seconds of the shooting, which lasted about 6 1/2 minutes. Peterson also arrived at the scene without a bulletproof vest or rifle and called for measures to lock down the school, the attorney told jurors.

"To sit in the calmness of a courtroom that is chill and mellow and try to go back and Monday morning quarterback is unfair and unjust," he said.