Newshub's National Correspondent Patrick Gower's new documentary On Hate looks into the Christchurch terror attack - and how the terrorist picked up his extremist views.
We know the gunman had been using the controversial website 4chan - but he told the Royal Commission that YouTube played an even bigger role in his radicalisation.
We don't know exactly what videos he watched but we do know he donated money in 2017 to Stefan Molyneux, described by his detractors as a far-right propagandist.
Molyneux circulated racist conspiracies unchecked on YouTube and at his peak had nearly 1 million subscribers.
Molyneux and fellow right-winger Lauren Southern supported some of the ideas behind the original 'great replacement theory', expressing these views to YouTube's global audience. It is the same conspiracy theory the Christchurch terrorist used as a justification for his attack.
"Both of them have a huge audience online and they believe that multiculturalism is a threat to the Western white world," explains Distinguished Professor Paul Spoonley, an expert on the extreme right.
"These are extreme YouTubers."
In 2018, the pair announced that they were coming to New Zealand on a speaking tour.
Many Kiwis weren't interested in letting them share their racially divisive views and the duo's speaking engagement was cancelled after large public protests.
It was the news story of the day and Gower wanted in. He arranged for the pair to come into the Newshub office for a sit-down interview about their beliefs.
Looking back at the footage, it's a decision he deeply regrets.
"There was no great big plan, and I didn't know a lot about them or the issue," Gower tells Prof Spoonley.
But the pair weren't interested in being interviewed, instead turning up with a "confrontational vibe", eager to expound on their far-right beliefs.
When Gower asked Southern if New Zealand's diversity made it a weak country, she responded by asking if he would "accept the diverse view that women should be stoned for the crime of being raped".
Gower knew that he was in trouble.
"In that single sentence, you've got the possibility that you would support people who are going to be stoned as a form of punishment, except that's not what multiculturalism is at all, so they've just redefined multiculturalism to be this threat and this threat coming from Islam," Prof Spoonley explains.
Gower then questioned Molyneux about whether different races are genetically weaker than others - and Molyneux began discussing his views on supposed racial IQ differences.
"Why did I let him carry on?" Gower asks himself in retrospect.
"He has a firm belief in the significance and relevance of eugenics, which is an argument about the genetic purity and the need to improve the genes of a particular 'racial group', but then it was translated into political environments such as Nazi Germany where it became a scientific justification for the genocide of a people," Prof Spoonley says.
"Both of these guys would deny that they are involved with Nazis, that they are responsible for violence, but they contribute to hate crime and hate speech that you see around the world. But as far as I'm concerned, they provide the background, they provide the reasons, they provide the mandate for people who do take it that extra step."
Prof Spoonley tells Gower that if he talks to people like Molyneux and Southern then ultimately "you're going to amplify and provide them with a platform".
"You do need to be well-versed in both their arguments and their strategies and how they do try to engage with the media, who they think are the enemy," he says.
Gower says he's spent his career trying to help people and make New Zealand a better place. Instead, he feels he helped spread their message.
"Knowing what's at stake, I actually personally find it distressing to watch this, knowing what came on March 15," Gower says.
Patrick Gower: On Hate is available to watch on ThreeNow.