Ardern said Tarrant was a licensed gun owner who bought the five guns used in the crimes legally.
Hundreds of people gathered in Nathan Phillips Square Friday evening to remember the victims killed in shootings at two New Zealand mosques.
"A category-A firearm holder can purchase the firearms without the magazines or the things that will enable them to be in the state that they were", New Zealand police commissioner Mike Bush told reporters, according to the Guardian.
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"The offender was in possession of a gun licence" obtained in November 2017, and he started purchasing the weapons the following month, she said.
"The individual charged was in custody 36 minutes from receiving the first call", she said.
Prime Minister Justin Trudeau also condemned the fatal shootings, saying the attack on people during prayers is "absolutely appalling".
"I believe many New Zealanders will be aghast that in our country someone can amass a cache of weapons like that discovered in this Christchurch tragedy", he said in a statement.
New Zealand police said 49 people were killed and 42 were being treated for wounds, including a four-year-old child.
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Cheddar's Scratch Kitchen: Order a homemade chicken pot pie in the restaurant, or one to-go, and receive a second one for free. Every Pi Day , my brother-in-law, a PhD math/physics guru, posts an endearingly nerdy treatise about pi on Facebook.
Despite mentioning Roof, it was Breivik, who her referred to as "Knight Justiciar Breivik", as a person he "took true inspiration from", wrote Tarrant.
Tarrant on Saturday was charged with only one count of murder, though Prime Minister Ardern assured the public that more charges will be added as the judicial process continues. Australia honoured the victims by lighting up some of the country's most famous landmarks, including the Sydney Opera House which projected the Silver Fern of New Zealand on its sails. Two explosive devices were also found in his auto.
Speaking to media in Wellington earlier, Ardern stressed that "now was the time for change".
He was remanded in custody to reappear in court April 5.
At least one of the weapons used by Tarrant was reportedly an AR-15 - the same semi-automatic rifle used in a number of mass shootings in the United States, including the 2012 Sandy Hook school killings in CT.
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She added: "I don't believe there is a deal out there that is better than we have now". Last night, along with most MPs, I voted against the Prime Minister's Deal.
Mr Graystone said he chose to stand outside the Medina Mosque on Friday because he "wanted to make sure that people know we can respond with friendship".
During her press conference, Arden said banning such weapons was "certainly one of the issues that I'm looking at with immediate effect".
"Regardless of how that result went, that wouldn't have been the most important part of my day. It will be hard to get past and I'm not sure how", Hindy said.
At first, Mr Taylor and his colleagues had no idea what was happening, initially believing the alarms, sirens and general panic sweeping through the New Zealand city were signs of another quake, similar to the 6.2-level seismic disaster that destroyed massive swathes of the city in 2011.
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The NFL free agency frenzy is underway and the opening day did not go well for the Houston Texans. With Morse's departure, the Chiefs will likely turn to Austin Reiter as their starting center.