Scott Israel the Sheriff of Broward County where the shooting took place said the deputy at the school chose to resign after Israel suspended him without pay.
“Scot Peterson was absolutely on campus through this entire event. He was armed. He was in uniform,” Israel said at a press conference.
"I am devastated. Sick to my stomach. He never went in," Sheriff Israel said.
When asked at the press conference what Peterson should have done, Israel said the deputy should have “went in, addressed the killer, killed the killer.”
“There are no words,” he said.
Peterson, who had worked for the sheriff's office since 1985 and was receiving an annual salary of $75,000, is yet to publicly comment on what happened. Police are reportedly guarding his home.
Trump, NRA solution: More guns
The revelation comes as US President Donald Trump earlier this week cast citizens with weapons as a solution to shootings. Trump also suggested arming school teachers with guns during a meeting at the White House on Wednesday.
The proposal has long been championed by the powerful National Rifle Association (NRA) gun lobby. NRA chief Wayne LaPierre on Thursday dismissed street protests and mounting demands to tighten America's permissive gun laws.
“They hate the NRA. They hate the Second Amendment. They hate individual freedom,” LaPierre said at the Conservative Political Action Conference in Oxon Hill, Maryland, near the nation's capital.
LaPierre said "opportunists" were using the tragedy to expand gun control and abolish US gun rights.
“Evil walks among us and God help us if we don't harden our schools and protect our kids” LaPierre said. “The whole idea from some of our opponents that armed security makes us less safe is completely ridiculous.”
Last week, Nikolas Cruz, an ex-student at Marjory Stoneman Douglas High School in Parkland, Florida, opened fire with an AR-15-style assault rifle, killing 17 people in his former school. It was the second-deadliest shooting at a public school in US history.
The Republican-controlled Congress last year revoked Obama-era regulations meant to make it harder for those with severe mental illness to pass FBI background checks for guns, saying the rule deprived the mentally ill of their gun rights.