It is, however, an offence in the Counter Terrorism Legislation Bill, currently before select committee, which the National Party supported at first reading.
Collins told RNZ this morning that she had texted Prime Minister Jacinda Ardern last night offering National's support to pass the bill into law under urgency.
Asked about her comments in 2013 about having no substantial or urgent concerns with New Zealand's counter terrorism legislation, she said it was "really unfair" to ask her about decisions from eight years ago.
"You are asking me to reach back without notes to go back and look at eight years ago at decisions made by the Cabinet," Collins told RNZ this morning.
She said she wasn't going to second-guess Cabinet decisions - which would have been made in a particular context, and following consultation - from eight years ago.
The horrific events of yesterday showed a need for an ability for a government to remove citizenship or residency from someone who had been granted it and later committed a violent crime, she said.
"It is a privilege, not a right. I am offering National's support to work constructively with the Government to make this change.
She said the Immigration Minister should be able to revoke a residency visa if the holder of the visa does something that would fail the "good character" threshold.
That would include being sentenced to a term of imprisonment of 12 months or more.
Under the Immigration Act, residency or permanent residency visas are cancelled if the holder is deported.
Reasons for deportation include committing an offence that could lead to a jail term of at least three months within the first two years of residence, or one that could lead to a jail term of at least two years within the first five years of residence.
Currently the Minister of Internal Affairs can remove someone's citizenship if they have taken on the citizenship or nationality of another country and "acted in a matter contrary to the interests of New Zealand", or had acted fraudulently to gain citizenship in the first place.
Would he have been in jail?
Yesterday Ardern said it was speculative to consider whether the terrorist would have been in jail rather than in the community yesterday if the gap in the law had been filled earlier.
Planning a terrorist attack is an offence in the Counter Terrorism Legislation Bill that would carry a maximum penalty of seven years' jail.
A conviction for this offence, if the bill had already become law before he was arrested, could have certainly landed the terrorist in jail after his sentencing in July this year.
Legal expert Andrew Geddis told RNZ that the man, a Sri Lankan national, could have been sentenced to jail anyway because he was convicted of possessing material that promoted terrorism.
This offence - of possessing objectionable material - can be punished by up to 10 years' jail.
But the judge decided to give him a supervision sentence, meaning he was allowed to be in the community with conditions, including undergoing a psychological assessment.
Geddis said it could not be known whether the judge might have chosen a jail term if the terrorist had also been convicted of planning a terrorist attack.
