Immigration officials had sought to revoke his refugee status in 2018, but he appealed and a final decision had yet to be made on whether he could be deported.
His uncertain immigration status was also the reason why the terrorist could not be identified until 11pm Saturday night, when it was lifted by a High Court judge, as anyone claiming refugee status cannot be identified by law.
It was unclear why the man could not have been detained for an assessment using the Mental Health Act, said former counter-terrorism advisor Paul Buchanan.
"He could have been, upon his release, immediately committed to an institution under the Mental Health Act in order to undergo that psychiatric examination. And he could have been held indefinitely until psychiatrists determined that he did not pose a threat to society.
"The PM said that every legal remedy was tried, but at least one, the Mental Health Act, was not tried. To me that is the big issue."
'Terrorism laws not the answer'
Meanwhile, stronger terrorism laws allowing those planning terrorists acts to be arrested were not the answer, Buchanan said.
"One of the things that the government does, repeatedly, is every time there is a terrorism-related anything, they move to expand the powers afforded the government under terrorism legislation. There's this constant push to grant the government more and more powers.
"The remedy is not to keep on expanding the powers of the state in this area called terrorism. The remedy is to have enough on the criminal laws, so that if there's clear evidence that someone wishes to do harm to others, or someone is preparing to do harm, that they can be arrested and charged under the Crimes Act."
Having separate terrorism charges gave offenders kudos and only elevated their cause, he said.
"You don't want to elevate these guys, you know, give them a bully pulpit in court, or make them martyrs through like-minded people by elevating the cause or the motivation, just focus on the crime."
However, Waikato University law professor Alexander Gillespie disagreed, saying the terrorism laws should be strengthened to include the planning of attacks.
"New Zealand made significant advances between what happened on March 15 and what happened yesterday..but there are still gaps.
"The first one is about the preparation of a terror offence, and that should be changed, the other big question that people will ask now is, if this person was a foreign citizen, what were they doing in this country when they were a terror risk?"
The terrorist was 22 when he arrived in NZ in 2011 and it was not known he held extreme views, Ardern said. He came to the police's attention in 2016 after he made concerning posts on Facebook.
