Until 2016, Cesar Altieri Sayoc Jr.’s life on social media looked unremarkable. On his Facebook page, he posted photos of decadent meals, gym workouts, scantily clad women and sports games — the stereotypical trappings of middle-age masculinity.

But that year, Sayoc’s social media presence took on a darker and more partisan tone. He opened a new Twitter account and began posting links to sensational right-wing news stories, adding captions like “Clinton busted exposed rigging entire election.” On Facebook, his anodyne posts gave way to a feed overflowing with pro-Donald Trump images, news stories about Muslims and Daesh (also called the Islamic State), far-fetched conspiracy theories and clips from Fox News broadcasts.

By the time he was arrested in Florida on Friday, charged with sending pipe bombs to at least a dozen of Trump’s critics, Sayoc appeared to fit the all-too-familiar profile of a modern extremist, radicalized online and sucked into a vortex of partisan furor.

In recent weeks, he had posted violent fantasies and threats against several people to whom pipe bombs were addressed, including Rep. Maxine Waters, D-Calif., and former Vice President Joe Biden. His vehicle, a white van plastered with right-wing slogans, came to resemble a Facebook feed on wheels.

“He went from posting pictures of women, real estate, dining and cars to posting pictures of ISIS, guns and people in jail,” said Jonathan Albright, research director for Columbia University’s Tow Center for Digital Journalism, using an alternative name for Daesh.

“It’s a remarkable change.”

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Twitter was warned at least once about Sayoc’s threatening behaviour but failed to act. On Friday, the company took down Sayoc’s accounts after he was named as a suspect.

Facebook, which also took down his account Friday, condemned his actions in a statement. “There is absolutely no place on our platforms for people who attempt such horrendous acts.”

But before Sayoc’s accounts were removed, The New York Times archived their contents. And a closer study of his online activity reveals the evolution of a political identity built on a foundation of false news and misinformation, and steeped in the insular culture of the right-wing media. For years, these platforms captured Sayoc’s attention with a steady flow of outrage and hyperpartisan clickbait and gave him a public venue to declare his allegiance to Trump and his antipathy for the president’s enemies.

On social media, none of this behaviour is particularly out of the ordinary. In fact, to many of his followers, Sayoc may have appeared to be just one of many partisan keyboard warriors working through their rage.

“There are tons of people like this,” said Shannon McGregor, an assistant professor of communication at the University of Utah who studies social media. “He took these memes to their most violent extreme, but this is a pretty big world on social media.”

The genesis of Sayoc’s partisan awakening may never be known, but hints of it first appeared on his Facebook feed in early 2016, as the primary season for the presidential election was starting.

That February, he posted a link to a conspiracy theory video on YouTube titled, “Is Barack Obama THE ANTICHRIST — 100% PROOF Is There!” Days later, he posted a second YouTube video, “Satan Sent Obama to Destroy America,” and a clip featuring Sean Hannity, the Fox News host, which was called, “MUST HEAR: Sean Exposes Illegal Immigrant Crime Stats.” He posted several anti-Obama videos multiple times on his feed, interspersed with stories about personal finance and his favourite soccer players.

By the summer, Sayoc’s social media activity was all politics, all the time.

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On Facebook, he posted stories from Infowars, World Net Daily, Breitbart and other right-wing websites. His posts, which rarely included commentary apart from the links, showed a fascination with Islamic terrorism, illegal immigration and anti-Clinton conspiracy theories. (On one post, a YouTube link, he wrote: “The Clinton have funneled 2 billion dollars through Clinton foundation.”)

In October, a month before Trump’s election, Sayoc posted a series of photos of himself at a Trump campaign rally, watching from the crowd in a red “Make America Great Again” hat.

Despite his prolific posting, Sayoc does not appear to have gained a wide audience. His Twitter account was followed by fewer than 1,200 people as of Friday morning, and although he had nearly 3,000 friends on Facebook, many of his posts were never commented on or shared.

He did, however, display an unusual tendency to post stories and images over and over again, sometimes dozens of times.

But while Sayoc may have been an outlier in frequency, the content he posted resembled the kind of highly charged outrage bait that is a staple of partisan internet circles. On social platforms, where polarized content is often better at generating engagement than nuanced conversations, there can be a temptation to veer into more extreme territory to stand out.

“People find people with similar interests, and it naturally leads them to encounters and relationships and information they wouldn’t necessarily find offline,” Albright said. “Being able to find similar communities can really lead you down a path of radicalization.”

In recent months, Sayoc’s behaviour changed. His posts took on a darker, more obsessive tone, often accompanied by threats of violence and gory images of bloody animal carcasses. No longer mistakable as an everyday internet partisan, he posted repeatedly about “unconquered Seminoles,” a reference to the tribe that he appears to have adopted. (It also appeared on his van.) And on Twitter, his messages turned dark and sinister.

He directed a tweet at Waters with a photo of what appeared to be her house. The message read: “see you soon.”

He sent another to Eric Holder, an attorney general under Obama, that read, “See u soon Tick Tock.” And he told Zephyr Teachout, a Democrat who ran unsuccessfully for attorney general in New York, that he had a surprise waiting for her. “We Unconquered Seminole Tribe have a special Air boat tour lined up for you here in our Swamp Everglades,” he wrote. “See u real soon. Hug your loved ones.”

Many recipients of Sayoc’s social media wrath most likely disregarded it, or wrote him off as just another overzealous troll. But the few who tried to sound the alarm appear to have been ignored. This month, Rochelle Ritchie, a Democratic political commentator, complained to Twitter that Sayoc had sent her a threatening message after she appeared on Fox News. The company replied that Sayoc’s tweet did not violate its rules against abuse.

On Friday, after Sayoc was named as the bombing suspect, Twitter apologized for the decision, saying Sayoc’s threatening tweet to Ritchie “clearly violated our rules and should have been removed.”

“We are deeply sorry for that error,” Twitter added.

Sayoc continued to post unabated until as recently as Wednesday, even as authorities were conducting a manhunt for the sender of the explosives that had been mailed to prominent Democrats. He sent a tweet to the Twitter account at the website TMZ that criticized Andrew Gillum, the Democratic candidate for governor in Florida, for raising campaign funds from Soros and other liberal donors.

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