The Australian who killed 51 Muslims at two mosques in New Zealand’s deadliest mass shooting has told an appeals court he felt forced to admit to the crimes because of “irrationality” due to harsh prison conditions.

Brenton Tarrant appeared in the Court of Appeal in Wellington on Monday, seeking to have his guilty pleas discarded, saying he wasn’t in a rational frame of mind at the time.

A panel of three judges will hear five days of evidence about Tarrant’s claim he was not fit to plead to the terrorism, murder and attempted murder charges he faced after the 2019 attack in Christchurch.

If his bid is successful, his case will return to court for a trial, which was averted when he admitted to the hate-fuelled shooting in March 2020.

He is also seeking to appeal his sentence of life without the chance of parole, which had never been imposed in New Zealand before.

Tarrant’s evidence on Monday about his mental state when he pleaded guilty was the first time he had spoken substantively in a public setting since he livestreamed the 2019 massacre on Facebook.

The self-declared white supremacist, migrated from Australia to New Zealand with a view to committing the massacre, which he planned in detail.

He amassed a cache of semi-automatic weapons, took steps to avoid detection and wrote a lengthy manifesto before he drove from Dunedin to Christchurch in March 2019 and opened fire at two mosques.

Along with 51 people killed, the youngest – a three-year-old boy – and dozens of others were severely wounded.

The attack is considered one of New Zealand’s darkest days and institutions have sought to curb the spread of Tarrant’s message through legal orders and a ban on possessing his manifesto or video of the attack.

There was tight security for Monday’s hearing, which severely limited who could view Tarrant’s evidence, including some media and those hurt or bereaved in the massacre.

Tarrant, who wore a buttoned shirt and black-rimmed glasses and had a shaved head, spoke on video from a white-walled room in prison.

Answering questions from a Crown lawyer and from his own lawyers, Tarrant, 35, said his mental health had deteriorated due to conditions in prison, where he was held in solitary confinement with limited reading material or contact with other prisoners.

By the time he pleaded guilty, Tarrant said he was suffering from “nervous exhaustion” and uncertainty about his identity and beliefs and that he had admitted to the crimes a few months before his trial was due to begin because there was “little else I could do”, he told the court.

Crown lawyer Barnaby Hawes suggested to Tarrant during questioning that he had other options.

He could have requested a delay in his trial date on mental health grounds or could have proceeded to trial and defended himself, Hawes said.

Hawes also put to Tarrant that there was little evidence in the documentation of his behaviour by mental health experts and prison staff that he was in any kind of serious mental crisis.

Tarrant suggested that signs of mental illness he displayed hadn’t been recorded and that at times he tried to mask them.

“I was definitely doing everything possible to come across as confident, assured, mentally well,” he told the court.

He said his behaviour “reflected the political movement I’m a part of”.

“I always wanted to put on the best front possible,” he said.

Tarrant agreed that he had had access to legal advice throughout the court process.

His lawyers have been granted name suppression because they feared representing him would make them unsafe.

Bids to appeal convictions or sentences in New Zealand must be made within 20 working days.

Tarrant was about two years late in seeking an appeal, filing documents with the court in September 2022. That was because he hadn’t had access to the information required to make it, he told the court.

The hearing is due to run for the rest of the week but the judges are expected to release their decision at a later date.

If they reject Tarrant’s attempt to have his guilty pleas discarded, a later hearing will focus on his bid to appeal his sentence.

-AAP