The FBI admitted on Friday it received a chilling warning in January from a tipster who said the gunman Nikolas Cruz could be planning a mass shooting, but that agents failed to follow it up.

But the attack has renewed calls for greater gun control with several survivors leading the charge.

One of them, 18-year-old Emma Gonzalez delivered a fiery address to a crowd of students, parents and residents in Fort Lauderdale.

“To every politician taking donations from the NRA, shame on you!” she thundered, assailing Trump over the multimillion-dollar support his campaign received from the gun lobby. The crowd chanted in turn: “Shame on you!”

“We are going to be the last mass shooting … We are going to change the law,” she insisted – slamming the fact that 19-year-old Cruz was able to legally buy a semi-automatic firearm despite a history of troubling and violent behaviour.

“The question on whether or not people should be allowed to own an automatic weapon is not a political one. It is question of life or death and it needs to stop being a question of politics,” Gonzalez said after her speech.

In Washington, the political response has made clear that the powerful NRA pro-gun lobby remains formidable, while Trump himself suggested the cause of mass shootings was a crisis of mental health – making no mention of gun control.

“If the president wants to come up to me and tell me to my face that it was a terrible tragedy and … how nothing is going to be done about it, I’m going to happily ask him how much money he received from the National Rifle Association,” Gonzalez said in her impassioned address.

“It doesn’t matter because I already know. Thirty million,” she said, citing the sum spent by the NRA to support Trump’s election bid to defeat Hillary Clinton.

She then ran through a list of the pro-gun lobby’s talking points – for example, that “a good guy with a gun stops a bad guy with a gun”, that no law could ever stop a madman intent on killing – answering each argument with “We call BS.”

The young woman’s powerful address immediately went viral, with her name a top trending topic on Twitter.

In addition to the FBI’s missteps, Cruz was also known to local police after his mother repeatedly reported him for violent outbursts, while records obtained by the South Florida Sun-Sentinel show authorities investigated Cruz in 2016 after he cut his arms on messaging app Snapchat and threatened to buy a gun.

The newspaper, citing Department of Children and Family Services documents, said the investigation came four days after Cruz turned 18 – legally an adult, and thus able to buy a firearm.

Investigators said there were “some implications” for the teen’s safety, but concluded that his “final level of risk is low as [he] resides with his mother, attends school and receives counselling” as an outpatient at a mental health centre, the Sun-Sentinel said.

Cruz later passed a background check, allowing him in February 2017 to buy the AR-15 rifle used in the massacre.

Trump spoke by phone with the Parkland mayor, the county commissioner and the principal of Marjory Stoneman Douglas High School to express his condolences and offer his support.

He then pivoted to politics with his allegations against the FBI – though the federal government’s investigation into allegations of Russian interference in the 2016 presidential race and collusion with the Trump campaign has been led by special prosecutor Robert Mueller since May.

There was no immediate response from the FBI to Trump’s latest allegation.

Mueller’s investigation has so far swept up four members of Trump’s campaign, with two agreeing to work for the probe under a plea deal.

On Thursday, Mueller indicted 13 Russians for allegedly running a secret campaign to tilt the vote, but did not accuse any Americans of knowingly taking part in that effort.