The armed officer on duty at the Florida school where a shooter killed 17 people never went inside to engage the gunman and has been placed under investigation, police have announced.

The Valentine’s Day shooting at Marjory Stoneman Douglas High School by a gunman armed with an AR-15 style assault rifle has reignited national debate over gun laws and school safety, including proposals by president Donald Trump and others to designate more people – including trained teachers – to carry arms on school grounds.

Gun-control advocates, meanwhile, have redoubled their push to ban assault rifles.

The school resource officer at the high school took up a position viewing the western entrance of the building that was under attack for more than four minutes, but “he never went in,” Broward County Sheriff Scott Israel, who is Jewish, said at a news conference on Thursday.

The shooting lasted about six minutes.

The officer, Scot Peterson, has been suspended without pay and placed under investigation, then chose to resign, Mr Israel said.

When asked what Peterson should have done, Israel said the deputy should have “went in, addressed the killer, killed the killer.”

The sheriff said he was “devastated, sick to my stomach. There are no words. I mean these families lost their children. I’ve been to the funerals. I’ve been to the vigils. There are no words.”

The suspect, 19-year-old Nikolas Cruz, has been jailed on 17 counts of murder and has admitted the attack.

Defence lawyers, state records and people who knew him indicate that he displayed behavioural troubles for years and he is known to have had a collection of weapons.

Politicians under pressure to tighten gun laws in response to the mass shooting floated various plans in the aftermath.

Four Jewish students and one Jewish teacher perished in the massacre. Earlier this week, Andrew Pollack, whose daughter Meadow was among the 17 people who died, told President Donald Trump the school shooting should be the last.

“My daughter is in King David cemetery,” Pollack said at the White House session convened by Trump, Vice President Mike Pence, and Education Secretary Betsy DeVos. “Never, ever will I see my kid, it’s an eternity.”

Pollack, surrounded by his three sons, vowed to work with Trump to stop school shootings. “How many schools, how many children have to get shot? It stops here, with this administration and me.”