The Independent Police Conduct Authority (IPCA) has confirmed it will conduct an investigation into the policing of the protest on Parliament's grounds earlier this year.
But it may not report back for more than a year, with the IPCA saying it is "anticipated the work will be completed and reported on by 31 March 2023".
The "investigation/review" will solely focus on the actions of police, including the management of intelligence, planning, decision-making processes, operational execution and engagement with protesters and businesses.
Also being examined: "The powers used to keep the peace, maintain public safety, enforce the law and provide community support and reassurance, and the tactical exercise of those powers. It also includes how police balanced the rights of protesters with the rights of other people throughout the course of the protest."
The investigation won't examine the policing of other protests in February and March "unless the policing of other protests influenced or informed in any way decision-making processes for the protest". It also won't look at issues around the spread of misinformation/disinformation on social media or the "political or socio-economic motivation" of complainants.
In a statement on Thursday afternoon, the IPCA said it had received nearly 1900 complaints - the largest number it has received about a single event or police operation.
"Many complaints are from individuals who were not present at the protest but are concerned about police actions or inactions," the IPCA said.
"Some are from individuals who were physically present and made complaints about specific or more general police activities, such as the lawfulness of their powers, use of force or particular tactics and treatment in custody."
Hundreds of people swarmed Parliament's grounds and surrounding streets in February, establishing campsites and blocking roads. Most were there in opposition to vaccine mandates and COVID-19 restrictions.
The occupation lasted until March 2 when police moved in, leading to a violent, fiery riot. Several officers were injured in that standoff, while a large number of demonstrators were arrested.
According to the IPCA, the protest was an "unprecedented event in New Zealand" and "one of the most significant policing challenges in recent years".
The purpose of the IPCA investigation is to provide "the public, police and other key stakeholders with an independent assessment of the information police had, the decisions police took, the tactics used and whether the approach taken to policing the protest as it evolved was lawful, proportionate, and appropriate".
Individual complaints will be addressed as part of the investigation and complainants will be contacted shortly to be informed of how their complaint will progress, the IPCA said. Individual investigations may be undertaken if required.
Prime Minister Jacinda Ardern earlier this week defended Labour's use of a majority on the Justice Select Committee to block a briefing by Police Commissioner Andrew Coster on the protest.
While National supports an IPCA investigation, it's concerned other elements of the protest outside police actions won't come under review.
"What about the role of the Speaker? What about the actions from Government Ministers?" National's Justice spokesperson Paul Goldsmith said. "What can the Police Commissioner tell us about what did and didn't happen?
"New Zealanders saw an unprecedented occupation and trashing of Parliament's grounds and its surrounding streets, followed by a fiery and riotous conclusion. How did it come to this, is the fundamental question.
"The existence of an IPCA investigation provides no justification for blocking every other form of inquiry. This is basic democratic accountability," Goldsmith said.
Ardern on Monday said it would be important to look at the IPCA terms of reference "before making a judgment as to whether or not everything that needed to be included or that we’d expect to be, is".
"If there are areas where... there's a public interest that we have a greater understanding and that we look into, then we'll look at that. But at this stage, we don’t have their terms of reference to make that call."
While the occupation was taking place, former top police negotiator Lance Burdett said the protesters had been aggravated by Speaker Trevor Mallard's use of sprinklers and speakers to try and deter protesters. The occupiers dug trenches to redirect the flow of the water and brought in speakers of their own to drown out the noise.