The Royal Commission of Inquiry into the Christchurch Mosque Attacks will not be completing its final report until nearly the end of November.
It had been due to wrap up at the end of July, but Minister of Internal Affairs Tracey Martin has extended the inquiry deadline.
Commissioner Jacqui Caine said good progress was being made, but the commissioners needed extra time to ensure the report is complete and authoritative.
They are still waiting on responses from some individuals and state sector agencies amid Covid-19 delays, but expect to receive all their responses in the next month.
The inquiry had planned to report back in December 2019, but the Commission itself, the Muslim group set up to assist it and the Federation of Islamic Associations requested an extension saying the original timeframe severely undermined the "complexity and gravitas" of the investigation.
Cabinet ministers then considered a November 2020 final reporting date with double the funding, but instead settled on 30 April.
When April rolled around however, Cabinet agreed to give the top level-inquiry two further months, after it asked for an extension.
The lockdown added further delays because responding agencies were diverting resources to the Covid-19 response, and staff could not access the draft report from home.
The shooter in the attacks has pleaded guilty to 51 charges of murder, 40 of attempted murder and one under the Terrorism Suppression Act and is due to be sentenced on 24 August, likely with significant precautions in place.
The inquiry's focus is on whether more could and should have been done to prevent the 15 March terrorist attack, and what could be done to prevent similar attacks in future, as well as investigating the terrorist and his activities before the attack.