The man who killed 51 Muslim worshippers at two mosques in New Zealand’s deadliest mass shooting told an appeals court on Monday that he felt forced to admit to the crimes because of “irrationality” due to harsh prison conditions at the time of his trial, as he sought to have his guilty pleas discarded.

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

If his bid is successful, his case would 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 Australian man, a self-declared white supremacist, migrated to New Zealand with a view to committing the massacre, which he planned in detail.

He amassed a cache of semiautomatic 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, dozens of others were severely wounded.

The attack was 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 possession of his manifesto or video of the attack.

Monday’s hearing took place under tight security constraints that severely limited who could view Tarrant’s evidence, which included some reporters and those hurt or bereaved in the massacre.

Tarrant, who wore a white button-down 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 lawyers representing him, 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 the Australian man 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.

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. (AP)