Jurors are due to begin a fourth day of deliberations Thursday in the trial of the former school resource officer who stayed outside during the 2018 massacre at a Parkland, Florida, high school -- 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 in what became the deadliest US high school shooting ever. His attorney argued the then-Broward Sheriff's Office deputy didn't enter the building under attack 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 and about whether he saw people fleeing the 1200 building.

The six jurors are set to meet again Thursday -- after deliberating so far for nearly 15 hours -- as Americans continue to grapple with mass and school shootings. About 200 attacks have unfolded on K-12 campuses since the Valentine's Day carnage at the Parkland school, a CNN tally shows, and more than 330 shootings with at least four wounded, excluding a shooter, have been recorded so far this year, the Gun Violence Archive reports.

If the jury finds Peterson not guilty of the six most serious charges -- second-degree felony child neglect, with up to 15 years in prison per count -- they will have to consider whether he is guilty of lesser crimes.

They could instead find him guilty of third-degree felony child neglect -- with up to five years in prison per count -- or culpable negligence, a misdemeanor. Peterson also faces a distinct charge of third-degree felony child neglect, for which jurors too could find him guilty of culpable negligence, and the perjury count.

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

To 'Monday morning quarterback is unfair'

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 killer 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 eight students -- seven of them minors -- and two school employees on the third floor of the 1200 building: Teacher Scott Beigel and students Meadow Pollack, Jaime Guttenberg, Cara Loughran, Joaquin Oliver and Peter Wang all were killed, while teacher Stacey Lippel and students Anthony Borges, Kyle Laman and Marian Kabachenko were wounded and survived.

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.