Man who claimed he was arrested for criticising police after Christchurch terror attack actually detained for illegal military-style firearm possession - IPCA

Police officers were justified in arresting a man who publicly criticised authorities after the Christchurch mosque shooting, with an independent investigation finding that wasn't the reason he was arrested.

The man was arrested after police received information he was in possession of a military-style semi-automatic firearm on March 17, 2019 - two days after the Christchurch terror attack.

After his arrest in Tauranga the man, identified only as Mr X, claimed he was arrested because "he had warned police about the risk posed by the man responsible for the March 2019 terror attack in Christchurch and following the attack he made public statements criticising Police for failing to act on that information", the Independent Police Conduct Authority (IPCA) says.

He was not arrested for that reason, however, and his arrest and detention were lawful. The IPCA said following the mosque shooting, police started a process of identifying New Zealanders who may hold extremist views and posed a risk.

"On March 17, 2019, two days after the attack, Mr X became a person of interest after he posted a recording on social media where he describes witnessing the shooter's behaviour at a gun club," the IPCA's report into the incident says. "On Saturday, March 23, 2019, police interviewed and then arrested Mr X. Police laid five charges of unlawful possession of firearms.

"The prosecution concluded with Mr X pleading guilty to one charge of possession of firearms without a licence."

Police said they take firearms offences extremely seriously.

"As the IPCA has determined the decision making around the man's arrest and prosecution was appropriate, with the man's public comments having no bearing on the actions taken by officers," assistant commissioner Richard Chambers said.