Official documents show the Royal Commission investigating the Christchurch mosque shootings wasn't on track to meet its April deadline before the country went into lockdown.
Cabinet last month agreed to give the top level-inquiry another two months to complete its investigation, after it asked for the extension.
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The Royal Commission said it wasn't going to meet its April 30 deadline because the nationwide lockdown had prevented staff from accessing parts of the draft report, stored in a secure network, from home.
But documents, released yesterday with thousands of pages of official papers, minutes and advice, showed the inquiry had indicated it wasn't on track to meet that deadline before the country went into lockdown.
Inquiry staff had told officials it had completed its investigation and "the circulation of the draft report to agencies and individuals" was well advanced.
"However, the logistical issues it has faced in obtaining information from agencies, the amount and sensitivity of information the Royal Commission has had to consider, and the processes it has had to adopt to protect sensitive information ... means that (even absent Covid-19) the Royal Commission will be unable to complete its report by 30 April 2020."
The paper showed the Royal Commission expected it would need another six weeks to complete the work and a further two to three weeks to prepare the report before it was handed over to the Governor-General.
This would have meant the report was submitted on June 30, it said.
"However, the current four-week level 4 Covid-19 response has caused, and is continuing to cause, delays for the Royal Commission meaning a 30 June 2020 report date would not now be realistic," the paper stated.
This was because responding agencies were diverting resources to the Covid-19 response and staff couldn't access the draft report during the lockdown.
"It therefore asks for a further six weeks in addition to the six additional weeks it would have needed to complete the report."
Cabinet agreed last month to extend the Royal Commission's deadline to July 31. It also agreed any additional funding the inquiry required would be covered by the Department of Internal Affairs until the end of this month.
When inquiry staff could access the draft report again, they would send "individualised extracts" to 21 relevant state sector agencies and 40 individuals, including current and former state sector employees, before including their responses in the final report, the documents said.
The documents also showed Tracey Martin, the minister responsible for the inquiry, told her Cabinet colleagues she had considered the need for the Royal Commission to provide assurances to affected communities and the public when considering the need for more time.
But the inquiry's terms of reference allowed it to make interim recommendations to ensure public safety, she said.
"No such recommendation has been made to date, but the ability to make such recommendations remains.
"These factors encourage me to conclude that any risk to public safety arising from a further delay in reporting date can be addressed by the commission, if necessary."
Martin added she was aware the further delay might be disappointing and concerning for members of Muslim communities, but was confident they would understand the implications of the Covid-19 pandemic on the inquiry's work.
The Royal Commission had planned to report its findings in December last year, but that was delayed to April 30 after requests from the commission itself, the Muslim group set up to assist it and the Federation of Islamic Associations.
They described the original timeframe as "unrealistic" and said it severely undermined the "complexity and gravitas" of the investigation.
Earlier, Cabinet papers showed ministers considered doubling the inquiry's funding and pushing its final reporting date out to November 2, 2020, but later settled on an April 30 deadline instead.