A few months after he turned 17 — and more than two years before he was arrested — Vincent Vetromile recast himself as an online revolutionary.

Offline, in this suburb of Rochester, New York, Vetromile was finishing requirements for promotion to Eagle Scout in a troop that met at a local church. He enrolled at Monroe Community College, taking classes to become a heating and air conditioning technician. On weekends, he spent hours in the driveway with his father, a Navy veteran, working on cars.

Twitter Terror: Arrests Prompt Concern Over Online Extremism

On social media, though, the teenager spoke in world-worn tones about the need to “reclaim our nation at any cost.” Eventually he subbed out the grinning selfie in his Twitter profile, replacing it with the image of a colonial militiaman shouldering an AR-15 rifle. And he traded his name for a handle: “Standing on the Edge.”

Twitter Terror: Arrests Prompt Concern Over Online Extremism

That edge became apparent in Vetromile’s posts, including many interactions over the last two years with accounts that praised the Confederacy, warned of looming gun confiscation and declared Muslims to be a threat.

Twitter Terror: Arrests Prompt Concern Over Online Extremism

In 2016, he sent the first of more than 70 replies to tweets from a fiery account with 140,000 followers, run by a man billing himself as Donald Trump’s biggest Canadian supporter. The final exchange came late last year.

“Islamic Take Over Has Begun: Muslim No-Go Zones Are Springing Up Across America. Lock and load America!” the Canadian tweeted on December 12, with a video and a map highlighting nine states with Muslim enclaves.

“The places listed are too vague,” Vetromile replied. “If there were specific locations like ‘north of X street in the town of Y, in the state of Z’ we could go there and do something about it.”

Weeks later, police arrested Vetromile and three friends, charging them with plotting to attack a Muslim settlement in rural New York. And with extremism on the rise across the U.S., this town of neatly kept Cape Cods confronted difficult questions about ideology and young people — and technology’s role in bringing them together.

Sorry, but your browser cannot support embedded video of this type, you can to view it offline.

The reality of the plot Vetromile and his friends are charged with hatching is, in some ways, both less and more than what was feared when they were arrested in January.

Prosecutors say there is no indication that the four — Vetromile, 19; Brian Colaneri, 20; Andrew Crysel, 18; and a 16-year-old The Associated Press isn’t naming because of his age — had set an imminent or specific date for an attack. Reports they had an arsenal of 23 guns are misleading; the weapons belonged to parents or other relatives.

Prosecutors allege the four discussed using those guns, along with explosive devices investigators say were made by the 16-year-old, in an attack on the community of Islamberg.

Residents of the settlement in Delaware County, New York — mostly African-American Muslims who relocated from Brooklyn in the 1980s — have been harassed for years by right-wing activists who have called it a terrorist training camp. A Tennessee man, Robert Doggart , was convicted in 2017 of plotting to burn down Islamberg’s mosque and other buildings.

But there are few clues so far to explain how four with little experience beyond their high school years might have come up with the idea to attack the community. All have pleaded not guilty, and several defense attorneys, back in court Friday, are arguing there was no plan to actually carry out any attack, chalking it up to talk among buddies. Lawyers for the four did not return calls, and parents or other relatives declined interviews.

“I don’t know where the exposure came from, if they were exposed to it from other kids at school, through social media,” said Matthew Schwartz, the Monroe County assistant district attorney prosecuting the case. “I have no idea if their parents subscribe to any of these ideologies.”

Well beyond upstate New York, the spread of extremist ideology online has sparked growing concern. Google and Facebook executives went before the House Judiciary Committee this month to answer questions about their platforms’ role in feeding hate crime and white nationalism. Twitter announced new rules last fall prohibiting the use of “dehumanizing language” that risks “normalizing serious violence.”

But experts said the problem goes beyond language, pointing to algorithms used by search engines and social media platforms to prioritize content and spotlight likeminded accounts.