The New Zealand Security Intelligence Service (NZSIS) has released a review of its decision making in the lead-up to the March 2019 terrorist attacks on Christchurch mosques.

Photo: RNZ/Vinay Ranchod

It has released all of the 135-page internal report, after putting out the executive summary several months ago, when the Royal Commission of Inquiry report was made public.

The Arotake review was ordered by the SIS after the attacks, and done by an independent expert from a Five Eyes partner.

It found the SIS systems were "broadly effective" to meet national security demands.

However, it lists five areas that could improve, including more resources to identify emerging threats, and sharpening up strategic intelligence analysis.

The national security system was faulted by the Royal Commission for a series of systemic failures before the attacks, though no one agency was identified as failing or accountable.

SIS Director-General Rebecca Kitteridge in a statement today said the agency had now "strengthened the way we identify and investigate national security threats, and has changed the mechanism through which leads are prioritised and assessed".

NZSIS director Rebecca Kitteridge speaking after the release of the final report by the Royal Commission of Inquiry into the terrorist attack, last year. Photo: RNZ / Sam Rillstone

The Arotake report - delivered to Kitteridge in mid-2019 after the expert got "unrestricted access to our staff, systems and records" - was a way for the SIS to internally scrutinise whether its work was up to scratch before the attack, while the Royal Commission carried on, Kitteridge said.

"In the interests of national security, my organisation needed an earlier indication of whether NZSIS could or should have known about the perpetrator of the attacks.

"We also needed an external expert to identify steps we could take to improve our ability to identify and disrupt such attacks in the future.

"It is important for New Zealanders to know that NZSIS sought to learn everything it could from this terrorist attack," Kitteridge said.