The searches generated a number of complaints about police actions.
Of those investigated by the IPCA, three searches were found to be unlawful.
In relation to two of those searches, police relied on the provisions of section 18 of the Search and Surveillance Act 2012.
This gives police the power to enter and search a place where they suspected an offence against the Arms Act 1983 had been committed and the person was incapable of having proper control of the guns or may kill or injure others.
The IPCA found in these cases those circumstances did not exist when the searches were conducted - therefore they were deemed unlawful.
In the third case police entered a house where they relied on section 14 of the Search and Surveillance Act 2012.
This provided the power to enter and search without warrant in circumstances where it was believed an offence was being or was about to be committed, or there was risk to life or safety that requires an emergency response.
Again, the IPCA found those circumstances did not exist at the time and therefore the entry into the house was unlawful.
IPCA chairman Judge Colin Doherty said he recognised that police were operating in an environment of "unprecedented and heightened risk" following the March 15 attacks, and there was a public expectation they take action to mitigate any further risks.
"It was therefore entirely appropriate that they set up an operation to eliminate or mitigate risk of further violence and ensure public safety.
"However, it is evident that in relation to these three searches, they did not give sufficient consideration to their legal powers of search and seizure."
Due to the high alert environment in which the police were operating at the time, the IPCA determined that the manner in which the searches were conducted did not require further consideration and focused only on the lawfulness.
The authority referred some of the complaints to police for investigation but also elected to conduct its own independent investigation.
Some cases are still active and are yet to be resolved.
All complaints that were deemed unlawful in today's findings came from the Canterbury region.
Police apology
Canterbury District Commander John Price said the searches were part of a "significant national security operation" in the aftermath of the mosque shootings.
"Following the terrorist attacks, a significant number of searches were carried out, in relation to possible persons of interest," he said.
The three searches scrutinised by the IPCA were part of that larger piece of work.
"I am confident that the officers involved in these three searches were acting with the best of intentions, and were absolutely focused on mitigating risk and preventing further harm in our community," Price said.
"Police acknowledge the IPCA's findings around legal powers of search and seizure in two of the three cases and shall be looking to work with the IPCA to seek a solution through lessons learned.
"Police have formally apologised to those involved."
The cases
Mr X came to police notice following an anonymous call to Crimestoppers alleging the Canterbury man was involved in white supremacy, anti-Muslim hate speech and racist behaviour.
Police discovered he had an historical mental health issue and was previously a member of a "far right-wing" Facebook group. He had also posted comments indicating he might be opposed to gun law reform.
On April 10 the man was at home with his partner and teenage son when four armed police stormed his house and "cleared" it before more officers entered.
The officer in charge of the search told Mr X his house was being searched under section 18 of the Search and Surveillance Act 2012. Police remained at his home for about three hours, leaving with a large number of his guns and licence. Mr X later complained that the search was unlawful, and he and his family were unlawfully detained.
Mr Y, also from Canterbury, came to the police's notice following information that he had been posting far right-wing material on a Facebook account. He held a firearms licence, but police did not know if he currently owned any guns.
On April 2 a group of armed police officers went to his house to search and seize any firearms.
Mr Y was at work at the time but his wife and family were home during the raid.
After speaking with Mr Y's wife and learning that there were firearms locked away in the house, police conducted a search under section 18 of the Search and Surveillance Act 2012.
While at the property the officer in charge received a phone call from Mr Y who was at his work. Mr Y was asked if he had any firearms with him. He told them he had an AR-15 rifle that he had recently bought. Mr Y agreed to wait at his work until police arrived.
The weapon was confiscated and after returning home to unlock his gun safe, more firearms were seized.
Police said the reason for the search was due to firearms being in the house and a belief that Mr Y had exhibited concerning behaviour and posed a threat to others.
In his case the IPCA did not consider there was reason enough to suspect the man had committed an offence. Alleged postings on Facebook were also not sufficient to suspect him incapable of having proper control of his weapons or that he would kill or injure anyone with a firearm.
In the third case a man known as Mr Z sparked concerns about his mental wellbeing after Facebook posts. As a result of that and background checks police visited him on March 28 at his residence that is occupied by a number of tenants who share common amenities.
When officers arrived at the Canterbury property they found the doors open but no one responding to knocks or calls. They walked in and knocked on bedroom doors, speaking to a flatmate.
The person took the officers to the man's bedroom to see if he was home.
While the room was empty, a drug utensil was spotted and the seized by police. Mr Z later complained to the authority about police entering his property and searching his room.
The IPCA found there was nothing to suggest that an emergency response was required to check on Mr Z and when they did not get a response to their knocking should have left and returned later.
