Security analyst Paul Buchanan said he had seen the manifesto of the alleged Christchurch shooter and his presence on right-wing platforms online.
"He is a very clear white supremacist who has been planning this for two years," he said.
Mr Buchanan called the Christchurch shooting a watershed moment in New Zealand history.
"This is about as bad as it can get because it shows we don't live in a benign environment ... we've been affected with the virus of extremism.
"The thing is it came from white supremacists and not the Islamic community, [they were] the target today."
Mr Buchanan said the mosque attack would raise a lot of questions within the security services because the "bulk of intelligence-gathering and efforts at prevention when it comes to terrorism have been directed at the Islamic community of New Zealand".
That meant that resources were not directed towards right-wing extremists.
"The intelligence services were looking the wrong way."
New Zealand succumbs to US 'homicidal politics of confrontation'
The shooter might have been part of a small cell who had some support in the Christchurch area, rather than a lone wolf, Mr Buchanan said.
He said this was because automatic or semi-automatic weapons weren't easily available in New Zealand without a licence.
"The weapon, from what I can tell, may have been modified. It takes some technical skills to modify a hunting weapon into something that's semi-automatic.
"He had high capacity magazines, he may have used a bump stock which was used by the Las Vegas shooter. These guys learn from each other."
The alleged shooter appeared to be on Twitter until a few hours ago.
"He was on right-wing platforms, including the platform that was used by the synagogue shooter in Pittsburgh last year. So, he's been out there with his views for a while.
"Why wasn't he flagged earlier and this whole episode prevented?"
He said this was a time to do some soul searching about how New Zealand had succumbed to "the homicidal politics of confrontation that we see in the US and Europe".
The first order of business would be to apprehend the subject and then his associates who helped him in his venture, he said. Thereafter it would pay to work back towards the planning and motivation.
Mr Buchanan said the shooter's skill set indicated he was either ex-military or had learned at the hands of someone else, who might be ex-military.
"Let's be very clear, Christchurch has a very active white supremacist community. A community that has attacked refugees and people of colour on multiple occasions over the last 20 years. This is the worst of them."