Prosecutors in the United States have delivered opening arguments in a case against a former sheriff’s deputy who allegedly failed to intervene in 2018 when a gunman attacked a high school in Parkland, Florida.

Scot Peterson, a former school resource officer for Marjory Stoneman Douglas High School, faces 11 criminal charges, including child neglect and culpable negligence, as a result of his behaviour. He has pleaded not guilty.

His trial, which began on Wednesday, is believed to be the first of its kind in the US. Never before has a law enforcement officer been criminally prosecuted for inaction during a school shooting.

But during the opening arguments, Peterson’s legal team warned a successful prosecution could set a dangerous precedent.

“He did everything that he possibly could with the limited information that he had,” said Mark Eiglarsh, Peterson’s lawyer.

Eiglarsh argued that Peterson had been “sacrificed” to abate public scrutiny over the Parkland incident. The attack, which left 17 dead and 17 more injured, remains one of the deadliest school shootings in US history.

“He was thrown under the bus,” Eiglarsh told the courtroom in Broward County. “He is not a criminal.”

The defence lawyer argued that Peterson’s prosecution was an attempt to deflect blame away from other officials, including Scott Israel, the Broward County sheriff at the time.

“A lot of heat was coming his way,” Eiglarsh said of Israel, who was removed from his elected position after Florida Governor Ron DeSantis had accused him of “repeated incompetence and neglect of duty”.

Florida’s legislature ultimately upheld the governor’s decision to suspend Israel from duty.

The prosecution, meanwhile, painted a different picture of what happened on February 14, 2018, when then-19-year-old Nikolas Cruz — a former student — opened fire in the school.

Broward County Assistant State Attorney Steven Klinger highlighted the fact that Peterson left his office 36 seconds after Cruz began to shoot, using an AR-15-style rifle to fire approximately 139 shots.

But Peterson ultimately remained outside the building where the attack was unfolding, Klinger alleged, taking shelter 23 metres (75 feet) away.

“He’s the lead security person at that school,” Klinger told the six-member jury. “He is trained how to handle a situation where he is the only law enforcement person there to handle an active shooter.”

According to Klinger, that gave Peterson the imperative to act: “You’ve got to get in there, and you’ve got to find the shooter.”

The shooting took place over approximately six minutes. Peterson, the prosecutor explained, held his position for nearly 40 minutes.

In addition to three misdemeanour charges of negligence and seven counts of felony child neglect, Peterson faces a misdemeanour count of perjury for his statements to investigators after the massacre.

At the time, Peterson explained that he only heard “two, three” shots coming from the building, which prosecutors have framed as a lie.

Defence lawyer Eiglarsh tried to complicate that narrative on Wednesday, highlighting the confusion that many witnesses at the scene said they experienced. Eiglarsh plans to call 22 of them to testify, he said.

He also explained that Peterson meant the “two, three” shots comment only as what he initially heard — not an overall assessment of the gunfire that day.

Peterson, like other witnesses, initially told investigators he thought the shooting had taken place outside, given how loud the attack was. He has since expressed remorse in the US media for what unfolded that day.

“Those are my kids in there,” Peterson told the TODAY Show in June 2018. “I never would have sat there and let my kids get slaughtered.”

He added: “It’s easy to sit there, for people to go, ‘Oh, he should have known that that person was up there,’” referring to the gunman.

Peterson faces a possible combined sentence of 97 years if convicted on all charges. In November, Cruz, the gunman, was sentenced to life without parole.

The outcome of the case could have repercussions beyond Florida, as school shootings continue to ravage the US. In the wake of an elementary school shooting in Uvalde, Texas, that killed 21 people, police officers have likewise faced investigations for failing to stop the violence.