Waikato University law professor Alexander Gillespie said he expected that Tarrant will face multiple murder charges.
Prime Minister Jacinda Ardern labeled the massacre "the worst act of terrorism on our shores" and immediately promised swift action, calling for gun laws to be changed.
Messages written in chalk are seen on a pavement in Christchurch on March 18, 2019, after 50 worshippers were killed last week in two mosque attacks.
A gun shop owner said the attacker purchased four guns from him through a "police-verified online mail order process", but it was unclear whether any of those firearms were used in the shootings.
Ardern has said the attacker used five guns, two of them semi-automatic, which were purchased with an ordinary gun license and modified.
Tipple said he supported Ardern's decision to reform gun laws as the Christchurch shootings had raised legitimate concerns.
Prime Minister Jacinda Ardern has urged citizens to hand in weapons before new gun laws are introduced.
Mr Tipple said the store did not sell the shooter the high-powered weapon that was used in the massacre. "Have owned a firearm for 31 years".
The organisers of New Zealand's largest gun show - the Kumeu Militaria Show, near Auckland - announced on Monday they had cancelled the event in the wake of the massacre and because of "elevated security risks".
Despite having tightened the rules in the 1990s after the last mass shooting, New Zealand has relatively permissive gun laws, with almost all of those who apply granted gun licences.
A Radio New Zealand report, based on police data secured through an Official Information Act request, said more than 99 per cent of people who applied for a firearms licence in 2017 were successful.
"Since I first heard about the atrocity on Friday afternoon I have reflected and reserved my thoughts", tweeted user @SirWB alongside a photo of a New Zealand police "arms surrender form". Only firearm owners are licensed, not weapons, so there is no monitoring of how many weapons a person may possess.
Like in the United States, most guns in New Zealand do not need to be registered. He was killed by police.
Ardern said the government had preliminary discussions about giving New Zealanders an opportunity to commemorate the victims, but any national memorial service will not take place this week. "You know I have lots of support, lots of love, lots of kindness from all of the New Zealand people".
There were 250 detectives and specialists across the country working on the investigation, said police. Duty lawyer Richard Peters, who represented him during the preliminary court hearing, told AFP the 28-year-old "indicated he does not want a lawyer".
He said "assurances were given" that once such content was pulled down, a regime would make sure it did not go back up.
Mr Peters told 9News that Tarrant appeared "lucid" and "seemed to appreciate what he was facing and why he was there".