The Christchurch mosque gunman required hospital treatment after accidentally shooting himself while cleaning a firearm in the months before the terror attack.
He was treated for injuries at Dunedin Hospital months before the March 15 attack last year - but hospital staff did not report the incident to police.
The injury was accidental after a bullet was not correctly chambered as he was cleaning or handling the weapon at his rented Dunedin home, the Herald has confirmed.
The self-shooting took place in mid-2018 and the gunman had bullet fragments in his eye and leg.
Southern District Health Board chief executive Chris Fleming said medical staff would welcome a debate around the guidance and support for clinicians facing such decisions - including the consideration of mandatory reporting.
"This was a horrendous tragedy that we all, as a society, must learn from," Fleming said.
"Disclosing gunshot injuries is not mandatory and it is impossible for clinicians to predict all outcomes."
The self-shooting incident caused damage to his rented Dunedin home and required the landlord to repair it.
Royal Commission report released publicly today
The self-shooting is believed to be detailed in today's public release of the Royal Commission of Inquiry into the mosque attacks.
Muslim leaders hope its recommendations will help prevent future terror attacks.
The Herald understands it is likely that Prime Minister Jacinda Ardern will speak at an embargoed press conference at secured "lock up" events from 10am to analyse the commission's findings.
Andrew Little, the minister in charge of the country's spy agencies, the Security Intelligence Service and the Government Communications Security Bureau, will also be in attendance - as will Police Minister Poto Williams, Minister of Justice Kris Fa'afo'i and local MP Megan Woods.
A total of 51 worshippers, including children, died in what is New Zealand's worst terrorist attack in the country's modern history.
Survivors have been told of the commission's findings.
Almost 21 months since the worst terror attack on New Zealand soil, the contents of the Royal Commission's 792-page report, examining how the tragedy was able to occur, can be publicly revealed at 2pm.
The inquiry, chaired by Commissioner Sir William Young, has been investigating the Australian mass killer Brenton Tarrant's activities before the March 15, 2019, attacks, including his travel in New Zealand and around the world, how he obtained firearms, his use of social media, and what relevant state sector agencies knew about him before the attacks.
It also looked at what actions state agencies took, what more they could have done, and whether some of them, such as intelligence agencies, were too busy looking at Islamic fundamentalism at the expense of the threat of white nationalism.
It's expected that the report – which took into account around 400 interviews, including one with Tarrant who was jailed for life without parole in August - will include many recommendations aimed at avoiding future similar tragedies.