During a trip to Europe in April and May 2017, mosque suspect Brenton Tarrant settled on the violent plan that he described as his "truth": he would commit a murderous attack that he believed would promote the cause of white nationalism.
In the almost two years that followed, Tarrant methodically prepared for his horrific massacre, amassing multiple shotguns and semi-automatic weapons and ammunition, plus combat clothing, an optical sight and a barrel-mounted strobe torch to confuse his victims.
After obtaining a gun licence in November 2017 and buying his first weapons the following month, he practiced shooting regularly at a South Otago rifle club, about 50km south of his home in Dunedin.
All the while, Tarrant, who had moved from Australia to New Zealand, apparently engaged in regular online discussion with fellow white nationalists, telling them before his attack: "Well lads it's time to stop s**tposting and time to make a real effort post."
Yet authorities in New Zealand and Australia failed to notice any sign that he may pose a threat and have admitted that they were not aware of him until he began livestreaming his murderous rampage on Friday, which left 50 people dead at two mosques in Christchurch.
Following the attack, Jacinda Ardern, New Zealand's Prime Minister, admitted failing and said Tarrant was "not on the radar of either the New Zealand intelligence agencies to the Australian agencies".
Authorities in both countries are now building a picture of the terrorist and his background and contacts with extremists. New Zealand security agencies will brief Ardern tomorrow.
But the attacks have raised questions about how this self-described introvert, who began considering the attack almost two years ago, went unnoticed and whether authorities have been too focused on Islamic radicalism at the expense of far-right extremism.
Professor Alexander Gillespie, an international security expert at Waikato University, said authorities had been "looking under all the wrong rocks".
"We were very concerned about jihadi terrorism and about gangs and about nationalistic Māori groups," he told the Telegraph.
"We were watching everyone else, but the attack came from the far-right. We were a little complacent. We didn't see it coming."
Tarrant's white supremacist views and his decision to launch a violent murderous attack on Muslims appear to have emerged from his travels in Europe in early 2017.
For the past four years, Tarrant has mainly been travelling the world, living off money he made from investing in a cryptocurrency and a small inheritance.
Around 2013, he moved to New Zealand, from where he travelled across Southeast Asia and China.
In a 74-page manifesto that he posted online shortly before his attacks, Tarrant said his views changed "dramatically" in April and May 2017.
Since the attack, authorities around the world have been investigating his various travels in recent years, particularly to identify any evidence of collusion. Turkish authorities are investigating trips there in March 2016 and September-October 2016 and Bulgarian authorities are looking into his travel there from November 9 to 15 last year.
Tarrant's precise movements from about 2013, when he is believed to have left Australia, until 2017, when he was known to have been living in Dunedin, remain unclear.
Following his decision to commit to a "violent, revolutionary solution", he began preparing for an attack. He initially considered launching an attack outside New Zealand, or in Dunedin, but eventually settled on Christchurch, which allowed for the possibility of attacking two mosques.
After purchasing guns, he joined the Bruce Rifle Club in South Otago in early 2018 and was well known among the hundred or so members.
Scott Williams, the club's vice-president, said Tarrant was friendly and helpful and seemed "as normal as anyone else".
"I think we're feeling bit stunned and shocked and a bit betrayed perhaps, that we've had this person in our club who has ended up doing these horrible things," he told the Otago Daily Times.
In Christchurch, the city remains in shock and the names and lives of the victims are beginning to emerge.
Gillespie told the Telegraph: "This will lead us to completely re-evaluate the way we look at threats. We were right to watch the other threat risks, but we have to be watching more."