Brenton Tarrant, 28, from Australia, was named in media reports in his home country as the gunman who appeared to have live-streamed the attack in Christchurch on Facebook as he shot victims in a mosque.
In a 74-page manifesto, believed to have been written by Tarrant, he describes anti-immigrant motives, saying the victims were a “large group of invaders” who he says “seek to occupy my peoples lands and ethnically replace my own people (sic)”.
Australian Prime Minister Scott Morrison confirmed that one of the people taken into custody by New Zealand authorities is an Australian.
The manifesto, posted online, features a series of questions and answers, and opens with one asking: “Who are you?”
The answer says: “Just a ordinary White man, 28 years old. Born in Australia to a working class, low income family.
“My parents are of Scottish, Irish and English stock. I had a regular childhood, without any great issues. I had little interest in education during my schooling, barely achieving a passing grade.”
He adds: “I am just a regular White man, from a regular family. Who decided to take a stand to ensure a future for my people.”
He describes himself as “a private and mostly introverted person” and admits he is racist, adding that he is an “Eco-fascist by nature”.
He said New Zealand was not the original choice for an attack, saying he only came to the country temporarily to plan and train.
On his planning for the attack, he wrote: “I begun planning an attack roughly two years in advance and an attack at the location in Christchurch three months in advance.”
Answering whether he supports Brexit, he wrote: “Yes, though not for an official policy made. The truth is that eventually people must face the fact that it wasn’t a damn thing to do with the economy.
“That it was the British people firing back at mass immigration, cultural displacement and globalism, and that’s a great and wonderful thing.”
The manifesto, which quotes from three British poets, also calls for London Mayor Sadiq Khan, whom he calls a “Pakistani muslim invader”, to be killed.
And he writes that he supports “many of those that take a stand against ethnic and cultural genocide”, including Finsbury Park mosque attacker Darren Osborne.
It also cites the rape of British women by “European women invaders” and includes links to the Rotherham sex abuse scandal.
On whether or not he is a supporter of US President Donald Trump, he wrote: “As a symbol of renewed white identity and common purpose? Sure. As a policy maker and leader? Dear god no.”
Sir Oswald Mosley is the person from history that he says he would most associate himself with.
An archive of a Facebook page thought to belong to Tarrant contained dozens of posts in the last week about multiculturalism in Europe, with several referring directly to the UK.
Among them were YouTube recordings of speeches by Sir Oswald.
The attacker’s rifles were covered in white-supremacist graffiti and he listened to a song glorifying a Bosnian Serb war criminal.
The number 14 is also seen on the rifles, possibly referring to 14 Words, which according to the Southern Poverty Law Centre is a white supremacist slogan linked to Adolf Hitler’s Mein Kampf.