New Zealand's government says no stone will be left unturned during a royal commission into whether authorities could have stopped the Christchurch terror attack that killed 50 people.
Since the mosque shootings on March 15, questions have been asked about how the lone man charged, 28-year-old Australian white supremacist Brenton Tarrant, was not flagged by security agencies on either side of the Tasman.
While New Zealand's government last week promised a probe would be held, Ardern on Monday confirmed it would be a royal commission - the most serious form of investigation possible into failures of government.
"In short, the inquiry will look at what could have and should have been done to prevent the attack. It will inquire into the individual and his activities before the terrorist attack," she told reporters in Wellington.
"While New Zealanders and Muslim communities around the world are both grieving and showing compassion, they are also quite rightly asking about how this terror attack was able to happen here."
Intelligence agencies, police, customs and the immigration department will be subject to investigation.
While the minister in charge of New Zealand intelligence, Andrew Little, has said increased attention had been paid to the alt-right and white supremacy in recent months, Ardern told media the commission would ask whether resources had been put in the right place.
"I want recommendations on how any such attack in the future could be stopped," she said.
Separately, her government is also turning its attention to social media companies.
A live-stream of the shooting continues to circulate online despite authorities social media companies like Facebook working to have it taken down. Facebook said it pulled down the video 1.5 million times in the first day after the attack.
"My question generally, across all of these platforms, is what can we put in place or have assurances around to ensure this doesn't happen again," Ardern said.
"We are as a cabinet having a conversation around meaningful change in the area of social media."
Several people are already being prosecuted for distributing the now-banned video in New Zealand and face up to 14 years' jail.
New Zealand's chief censor has also put a similar ban on a rambling 74-page "manifesto" posted by the gunman, spurring debate about free speech.
Tarrant - who will appear in court again next week on what is expected to be a raft of charges - is known to have participated on internet forums populated by right-wing extremists and foreshadowed the attack online, before live-streaming it using a helmet camera.
In Australia, South Australian senator Rex Patrick has called for a wide-ranging inquiry into far-right extremism following the attack.
"There is in fact a real dearth of hard information and analysis on right-wing extremist violence in Australia," he said on Monday.
Prime Minister Scott Morrison and opposition leader Bill Shorten will discuss the issue of violent online content with representatives from social media giants in Brisbane on Tuesday.
A New Zealand national memorial service has been announced for Friday.
Australian Associated Press