In a surprise court hearing, the man accused of the Christchurch mosque attacks has admitted charges of murder, attempted murder and terrorism.

Unusual events over the past two weeks might have prompted the mosque shooter to change his not guilty pleas to guilty.

Stuff understands Brenton Tarrant, who on Thursday pleaded guilty to murder and attempted murder charges resulting from his cold-blooded slaughter at Christchurch mosques in March last year, was visited by his sister Lauren, who also goes by the name Rosie Robinson, at Paremoremo Prison in Auckland in the last two weeks.

DAVID UNWIN/STUFF Professor Paul Spoonley wonders if the mosque gunman just couldn't face his victims' families in a trial.

Their conversation is unknown but Tarrant, who has been "up and down" according to sources, might have been helped by the interaction to come to a decision.

Rosie, a musician from Sandy Beach, near Coffs Harbour in New South Wales, shared with her brother a love of metal band Tool.

Also in the last fortnight, the mosque killer received the final disclosure of the police evidence against him, sources said. The scale of the overwhelming case against him may have focused his mind.

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The coronavirus lockdown measures might also have been a factor in his decision. The trial, scheduled for June 2, was expected to be delayed and Tarrant was facing more time in his cell under solitary confinement and extended uncertainty.

Massey University distinguished professor and sociologist Paul Spoonley, who is researching the Far Right and the aftermath to the March 15 massacre, said the shooter might have had a complete and genuine change of heart but he thought it unlikely.

Kai Schwoerer/Getty Images The accused gunman appeared in the Christchurch High Court by video link from Auckland.

"His actions to this point suggest it's not something like finding God but we don't know what has happened inside prison. He was a very committed white supremacist and it would be a major U-turn.

"What is unusual is that a trial gave him the opportunity to articulate his views yet again and he has forgone that opportunity.

"It's interesting to try to get inside his mind but he did something that we struggle with anyway because your or my moral compass is completely different."

He doubted that Tarrant would have been entirely prevented from using the trial to make statements and explain his cause.

"Whether [under severe restrictions] justice could be done or his defence would have agreed I don't know."

Spoonley said the shooter might not have been able to cope with encountering a courtroom made up of victims' families and had pleaded guilty to avoid that.

In a surprise court hearing, the man accused of the Christchurch mosque attacks has admitted charges of murder, attempted murder and terrorism.

One benefit of pleading guilty was he wouldn't encounter the details of the case and "what would be said about him personally".

It was always possible the gunman had an underlying psychological disorder that had been treated, with the result he realised the gravity of his actions, Spoonley said.

"These self radicalised shooters tend to have borderline psychological issues if not fully blown ones and it's a distinct possibility that condition has been treated.

"One of the things about these people is that they are not normally constrained by convention and normal interaction. You need to be a certain type of person to commit these sort of crimes in the first place and [his disorder] might have been untreated."

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

Although sentenced prisoners could expect some different surroundings and treatment, Spoonley doubted the authorities had offered Tarrant an incentive to plead guilty.

"If you've been to our maximum security prison they are very much about keeping prisoners separate and keeping control of them."

He was inclined to the belief no deals had been done as he couldn't imagine Corrections and the police negotiating.

"Imagine if that went public. It would engender especially from the Muslim community an enormous negative reaction."