For five years, the LynnMall terrorist has been supporting ISIS ideologies in New Zealand, from posting violent war videos to hiding hunting knives in his bedroom. But his family say they had no idea what he was up to. 

Newshub can't tell you his name yet, but authorities had a very clear picture of exactly who he was.

"There are many people with concerning ideologies. Very few of them reach the highest level of concern. And of those, it is this case that has caused us the greatest concern," said Police Commissioner Andrew Coster.

The Sri Lankan national was on the radar of several agencies, from police, and the Prime Minister, to the SIS. 

He arrived on a student visa in 2011 when he was 22. Five years later, he came to the attention of police for posting to Facebook about terror attacks and violent war videos. 

The posts continued, and a year later, he was arrested at Auckland International Airport, thought to be trying to get to Syria to join ISIS. 

Between 2017 and 2018, police found hunting knives and more objectionable videos and he was kept in prison while on bail.

Fast forward to July this year, the man was sentenced to 12 months' supervision in the community.

His family say they had no idea and are shocked by what he's done.

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"They’re obviously quite grieving at the moment. They were not aware of what this individual was doing and quite shocked to hear what has happened," said lawyer Davoud Mansouri-Rad, who previously represented the man. 

The man could not be deported and the reason is suppressed by the courts until later on Saturday night. 

"We'll release that as soon as we can but that story really tells itself as well," said Prime Minister Jacinda Ardern on Saturday.

The only option was for police to begin a secret surveillance mission. For 53 days, up to 30 specially trained officers watched his every move. 

"A motivated attacker even under surveillance is going to be hard to manage," said Coster.

Armed police have been guarding a mosque in Glen Eden since the attack happened. Detectives dressed in forensic suits and a photographer went inside today.

Neighbours say they've never had any problems.

"People is nice. There are not any problems," said one. 

"This is the first incident since 12 years. I've been here 12 years," said another. 

"Nothing wrong with this area. It's very quiet and peaceful," added a third. 

Between 30 and 50 people last year were investigated by the SIS in relation to violent extremism. Terror experts say this man posted so much online he was an obvious risk to security agencies.

"There are any number of people out there who talk about engaging in violence for ideological and other reasons and it's very difficult to know which ones are going to go on and act and carry it out," said Dr Chris Wilson from the University of Auckland.