Lawyers say an opportunity to deport the LynnMall terrorist was missed if he was considered a national security threat.

But the Government says that could not have happened legally because the man was appealing against the cancellation of his refugee status and they had to wait for the outcome.

Immigration New Zealand first considered over four years ago in August 2017 if Ahamed Aathill Mohamed Samsudeen was a threat to national security and therefore liable to deportation.

He was spoken to by police in April and May 2016 and issued a warning for publishing objectionable material, a High Court judgement from 2020 said.

He was then monitored by police, and seen making comments on news media articles that referenced violence against "scum" and "enemies".

Immigration lawyer Simon Laurent said the government did have the option to deport Samsudeen if they decided he was a threat to national security.

He said it would need the Immigration Minister Kris Faafoi to "certify" that a person constituted a threat or risk to security, and then the Governor-General to sign off on it.

"They would need to have some pretty solid grounds in order to proceed with deportation... it could have been reasonable suspicion, but I would suggest if ministerial certification was required, they would need some fairly cogent basis for making that direction. I'm not sure if they had that at that time," Laurent said.

While Immigration New Zealand was investigating a possible national security risk designation, they discovered his refugee application was fraudulent.

"This was on the basis that evidence found on his laptop by police indicated the individual had manufactured written statements from family members in support of his claim and embellished a medical report to align it with his claims," a statement from Minister Faafoi's office said.

Immigration NZ eventually cancelled his refugee status on those grounds in early 2019.

The man did have a legitimate right to appeal that decision on humanitarian grounds. He lodged that appeal in April 2019, which was to be heard by the Immigration and Protection Tribunal.

Laurent said the government may have let the cancellation on grounds of fraud run its course.

"One argument would be that process should have been exhausted first. The other thing is that it would have been less contentious for the government to have allowed him to complete that [Immigration and Protection Tribunal] process, rather than make a fairly bold step to direct his deportation because of being a national security threat."

The chairperson of the Auckland District Law Society's Immigration and Refugee Law Committee, Stewart Dalley, agreed. He said as a refugee, the man could have been forced to leave the country had he been deemed a significant enough threat.

But a spokesperson for the Immigration Minister Kris Faafoi said the law doesn't allow a deportation while the subject is appealing their refugee status being cancelled.

His appeal was lodged in April 2019. Samsudeen was also facing criminal charges, which only resolved in July 2021.

His IPT hearing was scheduled to happen this month, two and a half years later, but was ultimately never heard.

Prime Minister Jacinda Ardern agreed that it was not possible to deport the man while he was appealing, but said this was not a satisfactory situation.

She said the government would look whether that's appropriate for any future cases.

"I am just going to give us a bit of time to work through some of those options. It won't be quick," Ardern said on Monday.

"But I think it does warrant us exploring, because most New Zealanders would say 'if you acted fraudulently in gaining that status, and you're a threat to national security, surely there are some mechanisms [the government] can use there', so that's what we're exploring."

A further complication emerged around the time the man's criminal case wrapped up in July this year.

The following was issued by Jacinda Ardern as part of a timeline of the government's attempts to deport the terrorist.

"On 8 July 2021: Following consideration of the circumstances as they stood at the time, including updated research information about his home country, the outcome of the recent High Court criminal trial, the media reporting on the criminal trial and sentencing, and legal advice provided by Immigration New Zealand legal and Crown Law, it was determined that the individual would qualify as a protected person under the Immigration Act. Accordingly, it was unlikely he could be deported.

"Subsequently, Crown Law provided advice that INZ could not exercise its powers of arrest and detention pending the making of a deportation order, as the individual could not be detained for the purpose of deportation when that was not a realistic prospect."

A designation as a 'protected person' under international law gives the bearer a stronger right than a refugee to not be deported.

"National security does not override obligations preventing deportation of a protected person," the statement from Kris Faafoi's office said.