He announced his mass killing over social media and filmed it live on the internet. He shared a 74-page online manifesto peppered with sarcastic jokes about popular culture, repeating well-known internet memes and striving to mint new ones.

He even laid out his explanation in a “Q and A” format, as though in an interview, with asides to imagine the reactions.

“I am sure the journalists will love that,” he wrote, after answering, “yes,” to his own question, “Were/are you a fascist?”

The man accused of killing 49 people on Friday in a shooting spree at two mosques in Christchurch, New Zealand, identified in court papers on Saturday as Brenton H. Tarrant, is a 28-year-old body builder and personal trainer from the small town of Grafton, Australia. He is the son of a local garbage man who made a hobby of competing in Ironman triathlons.

But after the death of his father, in 2010, the suspect’s life took him in an unexpected direction. He invested in cryptocurrency, quit his gym job and took an idiosyncratic tour through North Korea, Pakistan, Eastern Europe, France and elsewhere.

And his travels — apparently solo — plunged him deeply into the online world of white-nationalist message boards.

Tarrant now appears to have become the first accused mass murderer to conceive of the killing itself as a meme; it seems he was both inspired by the world of social media and performing for it, hoping his video, images and text would go viral.

“Terrorism is the propaganda of the deed, and the terrorist is always as interested in his audience as his victim,” said Reid Meloy, a forensic psychologist and consultant to the FBI, paraphrasing the 19th-century Russian anarchist Mikhail Bakunin.

“But social media makes this vector much more powerful,” Meloy said. “We become host to the virus, and we accelerate its spread.”

The suspect’s parents were divorced early in his childhood, according to his father’s obituary in The Daily Examiner, of Grafton. Tarrant’s mother was not mentioned in the obituary, suggesting she may have been estranged from the father.

According to the obituary, the father competed in 75 triathlon competitions, including grueling Ironman triathlons in both Australia and Hawaii.

A woman with the same name as Tarrant’s sister played the drums in local rock bands, according to local news reports.

“Just a ordinary White man” from “a working class, low income family,” Tarrant wrote in his manifesto. “I had a regular childhood, without any great issues. I had little interest in education during my schooling, barely achieving a passing grade. I did not attend University as I had no great interest in anything offered in the Universities to study.”

It is unclear how he developed an interest in cryptocurrency but he wrote in his manifesto that his profits from investing in the cryptocurrency Bitconnect enabled him to travel.

Australian news outlets on Friday published a photograph of him with a tour group near the Samjiyon Grand Monument in North Korea. His manifesto alludes to visits to Poland, Ukraine, Iceland and Argentina as well.

References throughout his manifesto indicate that he was deeply immersed in white nationalist internet forums. He also appears to have developed a detailed interest in American politics.

To make his case for the effectiveness of memes, he pointed to a candidate in the 2016 Republican presidential primary he evidently found boring: “No one is inspired by Jeb Bush.”

“Were/are you a supporter of Donald Trump?” Tarrant asked himself in the manifesto. “As a symbol of renewed white identity and common purpose? Sure. As a policy maker and leader? Dear god no.”

He wrote that in some ways his attack was specifically aimed at an American audience.

“I chose firearms for the affect it would have on social discourse, the extra media coverage they would provide and the affect it could have on the politics of the United States and thereby the political situation of the world,” he wrote.

He hoped “to create conflict between the two ideologies within the United States on the ownership of firearms in order to further the social, cultural, political and racial divide,” thus “ensuring the death of the ‘melting pot’ pipe dream.”

He claimed he was not the type to seek fame.

“I will be quickly forgotten,” he added. “Which I don’t mind. After all I am a private and mostly introverted person.”

Tarrant is hardly the first accused killer to take a cue from social media or relish its reaction.

In 2015, a gunman in Roanoke, Virginia, sought to stream video of his killing of two local television journalists. The next year, a gunman attacking an Orlando, Florida, nightclub paused between shots to post on his own Facebook page.

But mass murderers often seek to innovate to outdo their predecessors, including through the exploitation of the media, Meloy, the forensic psychologist, noted, and Tarrant appears to have broken new ground in his self-conscious efforts to surf the waves of internet fandom.

He opened his video of his killing by reciting the slogan of the preteen and adolescent fans of a wildly popular YouTube channel largely devoted to humor and video games (although also sometimes touched by accusations of anti-Semitic or anti-Muslim bigotry): “Remember, lads, subscribe to PewDiePie.”

The creator of PewDiePie, Felix Kjellberg, posted on Twitter that he was “sickened” by the association, and in the process inevitably helped publicize the killing.

“Were you taught violence and extremism by video games, music, literature, cinema?” Tarrant asked himself, answering with sarcasm: “Yes. Spyro the dragon 3 taught me ethnonationalism. Fortnite trained me to be a killer and to floss on the corpses of my enemies.”

“Spyro the Dragon” and “Fortnite” are both popular video games, and “the floss” is a dance move popular with grade schoolers that characters in “Fortnite” sometimes perform.

He even urged other white nationalists to be creative.

“Paint, write, sing, dance, recite poetry. Hell, even meme,” Tarrant wrote. “Memes have done more for the ethnonationalist movement than any manifesto.”

He later recommended “edgy humour and memes” and appealing “to the anger and black comedic nature of the present.”

By his own account, he was radicalized during a one-month period during his travels in Europe in spring 2017.

On April 7 of that year, an Uzbeck asylum-seeker deliberately drove a truck into a crowd in Stockholm, killing five people in what authorities called an act of terrorism.

A month later, on May 7, the anti-immigrant French presidential candidate Marine le Pen — whom Tarrant described as “milquetoast” because she called for the deportation of only illegal immigrants — was defeated by the liberal President Emmanuel Macron.

“I found my emotions swinging between fuming rage and suffocating despair at the indignity of the invasion of France,” he wrote, referring to the immigrants he saw there.

His current address is in Dunedin, New Zealand, according to court papers. He wrote in his manifesto that he began planning an attack about two years ago and settled on the mosques in Christchurch two months ago.

He initially wrote a much longer manifesto, extending to 240 pages, he wrote. But he appeared to have had second thoughts.

“In a moment of unbridled self-criticism,” he wrote, “I deleted the entire work and started again, two weeks before the attack itself.”

He wrote that he intended to survive the attack. But as he wrote he appeared to wrestle with the likelihood that he would perish.

His questions to himself toggle between the present and past tense, as though he is unsure if he will be alive at the time of his imagined interview.

“I will see you in Valhalla,” he wrote at the end.

© 2019 The New York Times Company