But it also reflects wider examinations into a new crop of far-right groups whose rise has paralleled the increasing use of anti-immigrant fears to buoy right-wing political parties in the West.
Among the groups most adapt at stitching together the various strands of nativist anger and suspicion is the French-rooted Identitarian Movement, which promotes an alarmist message that Muslim migrants will one day overrun Western culture.
The Identitarian Movement apparently echoed Tarrant’s anger toward Muslim migrants, and is now at the center of international investigations as authorities try to piece together the elements that shaped Tarrant’s views.
A spokesman for the French wing of the Identitarian Movement told The Washington Post on Thursday that the suspect, Tarrant, had sent an unsolicited donation of about $1,200 in September 2017.
That is the second European group to acknowledge receiving money from the suspected attacker. Last month, Austrian authorities raided the home of an Identitarian-linked leader, Martin Sellner, who was given a donation of nearly $1,700 by Tarrant more than a year ago.
In Germany, meanwhile, officials said they were pursuing their own probes into other possible ties between Tarrant and German extremists.
In New Zealand, police are looking into possible ties between Tarrant and a Ukranian-born man, Troy Dubovskiy, 54, who apparently killed himself March 27 during a standoff with authorities. Police say a search of Dubovskiy’s home near Christchurch uncovered firearms, ammunition and “violent extremist content.”
It remains unclear, however, if Dubovskiy and Tarrant had any direct contact.
But Tarrant’s world increasingly appears informed by Identitarian influence.
In Germany, Austria and France, the group’s reach has so far been amplified by links to members of right-wing parties, established academic associations and other groups.
The Identitarian followers are careful to not publicly condone the use of violence. Its views, though, are all about a looming clash of cultures and religion — with only one winner possible.
“One of the dangers of this ideology is that it creates an imminent threat from the outside: a coming war if we don’t do anything about it,” said Austrian right-wing extremism researcher Julia Ebner, with the London-based Institute for Strategic Dialogue. “A violent escalation is part of their ideology.”
After arriving in Austria at the end of November from Central Europe, Tarrant traveled about 1,200 miles in a rental car on a week-long road trip. A key question — whether he used his travels to make contact with anti-Muslim extremists in Europe — remains unknown.
A direct link may not have been necessary to influence Tarrant’s thinking.
Identitarian movement members such as Sellner have aimed to win a battle for minds. They give frequent interviews, upload professionally produced videos to YouTube and have friends in powerful positions.
Two European security officials said that Sellner’s network has links to the far-right Freedom Party in Austria and its German equivalent, the Alternative for Germany (AfD). One of the movement’s German leading figures, for instance, works for an AfD member of parliament.
In Austria, the Freedom Party — which controls the Interior Ministry — has publicly vowed to confront extremist ideologies. But the Interior Ministry’s past decisions raise concerns about such promises.
In Feb. 28, 2018, Austrian police raided the country’s domestic intelligence agency, the BVT. Two European security officials — who spoke on the condition of anonymity because they were not allowed to speak to journalists — say that highly classified documents seized during the raid included details on Sellner’s direct or indirect links to members of the Freedom Party.
This previously unreported detail comes as the party has gone on a public campaign to deny any links to Sellner’s group.
A spokesman for the office of Austrian Chancellor Sebastian Kurz did not respond to questions about the February 2018 raid because of ongoing probes into it.
Sellner acknowledged that the group’s ideas may shape policies of Austrian far-right politicians, but he denied direct ties to any political party. “We don’t have any connections to them,” he said.
But experts believe overlap is inevitable by the way the group recruits: mainly targeting young academics and other politically active figures instead of violent extremists. One recruitment priority for the Identitarian Movement was the German military university, even though the Military Counterintelligence Service stopped those efforts.
In 2017, Sellner was among a group of far-right activists who chartered a ship to “defend Europe” from an influx of migrants across the Mediterranean Sea.
Sellner, who has acknowledged that he participated in neo-Nazi activities when he was younger, said his goal now is to stop what he fears is an “Islamization” in Europe.
He uses scaremongering phrases such as “mass immigration” and “population replacement” — a reference to the title of a 2012 book by right-wing French polemicist Renaud Camus, “The Great Replacement.” In his book, Camus writes that Europe’s white majority may eventually be replaced by immigrants from North Africa and elsewhere.
In Tarrant’s manifesto written before the attacks, the 28-year-old repeatedly cites the Great Replacement theory.
“For many years I had been hearing and reading of the invasion of France by nonwhites, many of these rumors and stories I believed to be exaggerations,” Tarrant wrote.
“But once I arrived in France, I found the stories not only to be true, but profoundly understated,” he continued.
For Jean-Yves Camus, a French scholar researching the European far right, it was important not to draw too many specific conclusions from Tarrant’s European travels.
“He came to Europe, he perceived that Europe was in a state of advanced decadence,” said Camus, who is not related to the author of “The Great Replacement.” “He was inspired by what he saw, but that doesn’t mean he was inspired directly by those he met.”
The Identitarian Movement in its present form originated in France nearly 15 years ago, said Romain Espino, a spokesman for Génération Identitaire, the name of the French branch.
“In terms of the way we work, each country is independent,” he said.
But the French movement, he acknowledged, has significant contacts with others in Italy, Germany and especially Austria, the home of Sellner.
Espino noted that he had seen Sellner on a number of occasions, including during a protest in Vienna and at the 2018 “summer university” hosted by Génération Identitaire. These events — which bring together movement members from across Europe — have occurred annually for the past 15 years, Espino said.
Sellner acknowledged that the United States was distinct from Europe, but he praised Trump for his “clear border control policy” and “antiglobalist agenda of national identity,” as well as his “national economic policy.”
In countries where Christian identity is part of mainstream politics, such as Germany and Austria, the group has doubled down on its emphasis on a conflict of cultures and religions. In more multicultural places, such as Britain, the messaging has been very different.
“There, they stayed away from anything that emphasizes race and ethnicity. Instead, they built their messaging around Muslim grooming gangs, for instance. They know where the grievances lie,” said Ebner, the researcher.
To gain access to right-wing extremist circles online and offline, Ebner has adopted false identities a number of times.
In October 2017, she attended an Identitarian Movement launch meetup in South London, with Martin Sellner and his American then-girlfriend and now-fiancee, Brittany Pettibone, among about two dozen attendees. Other members had traveled from France and Denmark, Ebner recalled.
“It’s clear from their training camps and militarized language that they prepare for a potentially violent scenario, even though they would never publicly condone violence,” she said.
Once Ebner went public with her 2017 experience and other related research, she started receiving death threats, she said.
Mekhennet reported from Cambridge, Mass., and McAuley reported from Madrid. Emanuel Stoakes in Christchurch contributed to this report.