Christchurch’s Muslim community is shocked and relieved after the gunman who killed 51 people at two mosques on March 15, 2019, pleaded guilty.

This story was originally published on RNZ.co.nz and is republished with permission.

Legal experts say the Christchurch mosque shooter will "undoubtedly" spend life in prison - likely with no parole - and there's a chance his jail time could be served in Australia.

After a surprise admission of guilt on Thursday, Brenton Tarrant will be sentenced for 51 murder charges, 40 attempted murder charges and one of engaging in a terrorist act.

A sentencing date is yet to be set as the courts work through ongoing disruptions from the nationwide Covid-19 lockdown, and consult with victims of the attacks and their families.

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Auckland University of Technology law professor Kris Gledhill said there was no doubt Tarrant would be sentenced to life imprisonment. But the main decision for the judge would be setting the minimum non-parole period.

"It's got to be at least 17 years because it was a terrorist murder and it involved more than one victim. But the Sentencing Act also says that if the judge feels the needs of punishment are such that there should be a sentence of life that means life, then the judge can impose such a sentence," he said.

STACY SQUIRES/STUFF Experts say the gunman could be the first person in New Zealand to get a life sentence with no parole.

It would be the first time a life sentence with no parole will have been imposed in New Zealand.

But University of Waikato law professor Alexander Gillespie said the judge would have a strong case for preventing the murderer from ever going back into the public.

"This law was created to deal with the worst of the worst crimes. And I can think of no part of New Zealand history when we've had a crime of this kind of repugnance," he said.

After sentencing takes place, some countries have a policy allowing their citizens who are in prison elsewhere in the world, to be transferred back home.

Gillespie said Australia was one of those countries, and there was a small chance it could offer to take Tarrant into their prison system after he was sentenced.

"It is 90 percent certain, [in] my mind he's going to do his time in New Zealand. But the Australians have a policy and they may reach out. I don't think they'd want to embarrass the government if it happened - I imagine they'd make a quiet offer behind closed doors and say, 'look, if you want to, we will respect the sentence of him being in jail forever, but he does that in Australia'. That wouldn't surprise me."

In the meantime, Police Commissioner Mike Bush said the murderer's guilty plea would free up valuable police resources.

"We've had a very large prosecution team, both Police and Crown, working extremely hard on this since 15 March. It means they can now focus all their attention on the victims. I think the most important thing out of this is the impact on those victims. That they don't have to relive this through a court trial," he said.

The guilty plea will not affect the Royal Commission of Inquiry into the mosque attacks.

The commission says its role isn't to inquire into the guilt or innocence of any individual charged, though the news is significant for survivors and families.

Tarrant has been remanded in custody and will appear in court again on 1 May for a procedural hearing.

This story was originally published on RNZ.co.nz and is republished with permission.