Local sheriff Scott Israel said the officer in question has resigned after initially being suspended
An armed officer was at the scene of the Florida school shooting but failed to confront the gunman, local officials have said.
17 people were killed in the shooting at Marjory Stoneman Douglas High School in Parkland last week.
In a press conference yesterday, Broward County Sheriff Scott Israel said Scot Peterson - a school resource officer - was on campus during the shooting.
He was armed and in uniform.
Sheriff Peterson explained: "After seeing video, witness statements, and Scot Peterson's very own statement, I decided this morning to suspend [him] without pay, pending an internal investigation. As is his right, Scot Peterson chose to resign, because he has the necessary time with the agency and meets the requirements of retirement. He resigned / retired."
"What I saw was a deputy arrive at the west side of building 12, take up a position... and he never went in."
Sheriff Israel dismissed speculation that the deputy hid in a classroom, saying he instead remained outside the building during the shooting.
However, he suggested the officer should have entered the building and confronted & killed the shooter.
The sheriff confirmed the deputy 'clearly' knew there was a shooting.
Asked about his own response to the latest revelations, Sheriff Israel added: "Devastated. Sick to my stomach. There are no words. These families lost their children, they lost coaches.
"I've been to the funerals [...] I've been to the vigils... There are no words."
Sheriff Israel also confirmed that two other deputies have also been placed on restrictive jobs for not acting on 23 calls sent to the sheriff's department during the past several years.
19-year-old suspect Nikolas Cruz has confessed to carrying out one of the United States' deadliest school shootings, officials said last week.
The shooting has reignited debate about US gun laws.
It has provoked a youth-led movement around the country, with teens - including Parkland survivors - and parents leading calls for stricter gun controls.
Donald Trump, meanwhile, has raised the controversial prospect of arming some teachers.
The head of the powerful National Rifle Association (NRA) lobby group has accused gun control advocates of politicising the country’s latest school shooting