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 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.
US senator Marco Rubio of Florida said a visit to Stoneman Douglas prompted him to change his stance on large capacity magazines. 
The Republican insisted he is willing to rethink his past opposition on gun proposals if there is information the policies would prevent mass shootings.
“If we are going to infringe on the Second Amendment, it has to be a policy that will work,” Mr Rubio said.
State senator Bill Galvano, who is helping craft a bill in response to the shooting deaths, said an idea gaining traction is a program that would allow local sheriffs to deputise someone at a school to carry a gun on campus.
Mr Galvano insisted the idea is not the same as arming teachers. He said the program would be optional and the deputised person would have to be trained by local law-enforcement agencies.
A day after an emotional meeting with survivors and their families, Mr Trump tweeted his strongest stance yet on gun control.
He said he would endorse strengthening background checks, banning “bump stock” style devices and raising the minimum age to 21 for buying certain rifles.
At a conference of conservative activists on Thursday near Washington, vice president Mike Pence said the administration would make school safety “our top national priority” after the shooting at the school in Parkland, Florida.
Calling school shootings “evil in our time,” Mr Pence exhorted those in positions of authority “to find a way to come together with American solutions.”
It was a markedly different tone than that deployed on stage minutes earlier by NRA Executive Vice President and CEO Wayne LaPierre, who delivered an unbowed defense of gun ownership and lashed out at Democrats — saying they are using the tragedy for “political gain.”
“They hate the NRA. They hate the Second Amendment. They hate individual freedom,” Mr LaPierre said.
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