Utøya, Charleston, Christchurch and Poway. In each case a lone gunman used a legally-acquired firearm in a calculated attempt to kill as many unsuspecting strangers as possible. And, over the weekend, we can now add to this El Paso.
But these are not the actions of isolated and deranged lone wolves. Rather, they are part of a lone wolfpack of white supremacists spawned in the dark corners of the internet. These killers don't see themselves as lonely, and indeed explicitly consider themselves members of a fascist brotherhood.
This brotherhood's actions are become increasingly frequent, with three attacks in the last six months. They now appear to pose the largest domestic terrorism threat faced in developed countries. So far this year Islamic terrorism - often used as a rallying cry demanding revenge by the lone wolfpack - has killed precisely zero people in OECD countries. But the wolfpack? Seventy-four and counting.
Part of this differential is down to a vigorous crackdown by law enforcement and tech companies against the likes of Islamic State. But it is also down to authorities incorrectly writing off the actions of white supremacist terrorism as isolated incidents, when clearly there they are part of a single movement.
I recently spent three months at Cambridge University unpicking a string of linked mass-shootings in a bid to understand where Brenton Tarrant and the shocking event in Christchurch on March 15 came from.
As part of my research, I spoke to officials from the United Kingdom's Home Office responsible for tackling extremism, counter-terror police, symbologists, historians of fascism, political scientists who dedicated their lives to the study of the radical right, and even met a musicologist in Edinburgh to talk about computer game soundtracks.
I focused my study on a handful of killers whose manifestos provided both quality primary evidence and, given their political motivations, self-selection as terrorists. I read radioactive manifestos ranging from the five slur-ridden pages of Charleston church shooter Dylann Roof to the largely plagiarised and bloated, 1518-page magnum opus of Norwegian mass-murderer Anders Breivik. I even forked out $102.20 to the Office of Film and Literature Classification to legally peruse the propaganda document left on 8chan by Tarrant on March 15.
For several afternoons in May I sat in a supervised room at the university's towering library in order to read an original copy of The Turner Diaries , a race-war potboiler which ends happily with 90 per cent of humanity genocided to allow for an Aryan revival in Los Angeles. This book would prove depressingly useful in spotting fascist shorthand and symbology.
I learned from social scientists the profile of more generic solo-actor terrorists. They're mostly socially maladjusted young men who are violent to their intimate partners, or who have never had one. Their move from radical ideas to action is often triggered by a personal or domestic shock, and they have access to firearms. They're not members of violent groups, but sometimes try to join and are rejected, and are often found hanging around the fringes.
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The common thread in specific wolfpack killings is not defined by their targets - which range across progressive youth politicians, black churchgoers, Muslim refugees and perceived Hispanic immigrants - but rather who the perpetrators see as their in-group.
They are all young white men, who see their dominance - characterised as "European identity" - as facing a threat so existential that peaceful democratic solutions are seen as either hopeless or part of the problem. Violence, chiefly indiscriminate and shocking violence designed to spur polarisation and retaliation, is seen as the only solution.
Breivik is in many ways Patient Zero. His long-planned bombing and shooting rampage which killed 77 in 2011 is deified online in anonymous Discord and 8chan channels. He is, in language cribbed from computer gaming, said to be the holder of the current "high score". Mass murder has become gamified.
Roof was evidence that radicalisation can occur solely online, no longer requiring face-to-face meetings, with him crediting a single white-power webpage for his conversion to violence. The recent shootings in Poway and El Paso - which both directly credit Tarrant and copy his format of self-promotion - are signs the contagion is spreading faster than fibre.
But can this spate be stopped? Understanding the links between these killers and their shared community is essential in order for society and authorities to respond. And this response needs to be comprehensive rather than the piecemeal approach to date. Action needs to be taken both on and offline.
One observation, which should be uncontroversial everywhere except for the United States, is that all four cases I examined - and the recent shooting in El Paso - involved killers who had purchased the firearms used in their attacks legally. Gun-control, particularly of large-calibre weapons with high-capacity magazines, is the low-hanging fruit of terrorism prevention.
The decision this week by security firm Cloudflare - whose support was essential in keeping controversial sites online - to cease work with 8chan is part of the online solution. It is noteworthy that the only previous site Cloudflare had withdrawn services to was Stormfront - a openly white supremacist site which counted amongst its users Breivik and Roof.
Curtailing of 8chan will not prevent the white supremacist community organising - lone wolves will migrate elsewhere - but it will make it harder for new recruits to first join or stumble across it. The most effective point of intervention has to be before the first red pill is taken.
After three months down a dark rabbit hole, the notorious manifestos I read no longer stood out. In parts of the internet, and even on YouTube, their toxic views and logical end-point of violence were the mainstream. It's a conclusion the Norwegian police reached several years ago: "There were a lot of people worse than Breivik on these sites".
Matt Nippert is a New Zealand Herald investigative reporter who recently concluded a term as a press fellow at Wolfson College at Cambridge University.