If Brenton Tarrant is not charged under the Terrorism Suppression Act, it is hard to see when it would ever be used, a legal expert says.
Fifty people have died in the Christchurch mosque shooting on Friday, the worst terror attack in New Zealand history.
So far Brenton Tarrant has only faced a single murder charge when he appeared in Christchurch District Court on Saturday morning.
But further charges will follow and they could be terror-related, Otago University law professor Andrew Geddis said.
"Given we've been calling this a terrorist act, the prime minister said this is terrorism, if our legal system can't reflect that in the charges that are laid, then it makes us wonder why we even have the charge on the books," Mr Geddis said.
"Under the Terrorism Suppression Act a charge of engaging in a terrorist act, if that charge isn't used in these circumstances, it's hard to see when it would ever be used," he said.
Whatever happens, the accused gunman will be spending a long time in jail, Mr Geddis said.
"The murder charges that he faces will probably have a minimum non-parole period of 17 years, because of the fact this was inspired by, it appears, terrorism.
"There's every possibility it will be a much, much longer non-parole period than that."
He could also face a life sentence without parole, he said.
"There's the possibility under law changes from 2010 of a life without parole sentence which would mean he would literally spend the rest of his life in jail.
"If he ever is released, then he is deported to Australia."
There is a chance the accused will defend himself, Mr Geddis said.
"One of the worries is he may try to use this trial to engage in some sort of political grandstanding, I suspect the judge will be quite careful to avoid that."