After 18-year-old Devon Arthurs converted to a violent, fundamentalist version of Islam about a year ago, he didn’t stop posting on the white supremacist messaging board he frequented. Nor did he avoid sharing a house with three roommates, who he later told police were all neo-Nazis.

For a time at least, these adherents of seemingly opposing extremist ideologies appeared to coexist under one roof in an upscale condominium complex in Tampa, Florida.

Now, however, Arthurs is in jail on murder charges, one roommate is in a federal detention center on charges of possessing explosives, and the other two roommates are dead.

Tampa Police Devon Arthurs told police he killed two of his roommates because they "disrespected his Muslim faith."

Last Friday, Arthurs walked into a nearby smoke shop with a gun and held three people hostage. When police arrived, they negotiated for the release of the hostages. Several minutes later, Arthurs surrendered.

He made references to “Allah Mohammed” during his arrest, according to the police affidavit, and then led police to his apartment across the street. Inside were the bodies of two of his roommates: 22-year-old Jeremy Himmelman and 18-year-old Andrew Oneschuk.

Arthurs later gave a full confession, according to a police affidavit, explaining that he and his two slain roommates, along with a third roommate, Brandon Russell, had all “shared a common neo-Nazi belief” until Arthurs’ conversion to Islam. The families of Himmelman and Oneschuk have strongly denied that the two were neo-Nazis.

Arthurs told police he shot Himmelman and Oneschuk because they “disrespected his Muslim faith.” He had “become angered by the world’s anti-Muslim sentiment,” the affidavit stated, and thought the murders would “bring attention to his cause.”

He also accused his roommates of plotting a domestic terror attack. When federal authorities subsequently searched the apartment, they discovered a package containing “explosive precursors” addressed to Russell, along with other bomb-making materials.

And in Russell’s bedroom, FBI agents found Nazi propaganda and a framed photo of Oklahoma City bomber Timothy McVeigh.

STR New/Reuters Timothy McVeigh was executed in 2001 for blowing up a federal building in Oklahoma City, killing 168 people. Authorities found a framed photo of McVeigh and Nazi propaganda in Brandon Russell's bedroom.

Russell, a 21-year-old Florida National Guardsman, was later arrested in Key Largo. Court documents state that he admitted to being a leader of the same neo-Nazi group of which Arthurs had once been a member: the Atomwaffen Division.

Earlier this week on an Atomwaffen Division message board, members mourned Himmelman and Oneschuk, posting photos of their “fallen Aryan brothers.” Many also argued that Russell should have dealt with Arthurs long ago.

Russell, one member wrote, was “sympathetic towards Salafism,” the ultra-conservative brand of Sunni Islam Arthurs had embraced, “and its [sic] come back to ruin his life basically.”

The Atomwaffen Division is a small group, known previously to the Southern Poverty Law Center and Anti-Defamation League only for posting racist recruitment flyers on college campuses.

But in January a “source” close to the group spoke to Radar magazine, detailing the Atomwaffen Division’s penchant for celebrating Islamic extremism.

The source told the magazine that the Atomwaffen Division often used the slogan “Osama was Right” and that its leader had praised Omar Mateen ― the man who massacred 49 people at a gay nightclub in Orlando in 2016 before declaring allegiance to ISIS ― as a “hero.”

When Arthurs converted to Islam, a friend told the Tampa Bay Times, Atomwaffen Division members didn’t immediately kick him off the group’s message board, even when Arthurs listed his political affiliation as “Salafist National Socialism.” They made fun of him, but he seemed to still be largely ingratiated with the group.

And even earlier this week, while many Atomwaffen Division members memorialized Arthurs’ alleged murder victims, at least one member of the message board appeared to condone his crime.

“He shouldn’t have done what he did but I’m not gonna shit on him for it,” someone wrote. “Islam openly commands to kill nonbelievers if they are at war with Islam and right now the U.S. is at war with Islam so when American Kuffar die it’s nothing I’ll get upset over.”

“Fuck off... you race traitor Muslim cunt,” another member responded.

The administrator for the Atomwaffen Division’s message board, hosted on IronMarch.org, also made an announcement this week: “All Muslims have been isolated and ejected from the group.”

The story of a neo-Nazi in Florida converting to Islam and then embracing a violent, fundamentalist version of the religion might sound anomalous, even absurd. But experts say what happened with Arthurs isn’t unheard of.

Moreover, there’s often ideological crossover ― and even mutual admiration ― between neo-Nazis and Islamic extremists, even if many in the neo-Nazi community are rabidly Islamophobic.

Brian Levin, director of the Center for the Study of Hate and Extremism at California State University at San Bernardino, pointed to the story of Ahmed Huber, a Swiss neo-Nazi who converted to Islam and was later accused by the U.S. government of funneling money to al Qaeda.

A 2002 CNN segment shows the inside of Huber’s study, where he proudly displayed photos of Adolf Hitler and Osama bin Laden.

Levin told HuffPost that Huber, who died in 2008, embodied many of the shared ideologies of neo-Nazis and Salafist jihadis. Namely, he was anti-American, anti-Semitic, and against the meddling of Western powers in other countries.

Then there’s David Wulstan Myatt, a prominent neo-Nazi in Britain who converted to a Salafist jihadi brand of Islam in the early 2000s.

His new religion, Myatt wrote in an essay explaining his conversion, was “the only force that is capable of fighting and destroying the dishonour, the arrogance, the materialism of the West.”

“For the West, nothing is sacred, except perhaps Zionists, Zionism, the hoax of the so-called Holocaust, and the idols which the West and its lackeys worship, or pretend to worship, such as democracy,” he wrote.

And in February of this year, a man known only as “Sascha L.” was arrested in Germany for attempting to kill police with explosives.

Authorities later uncovered evidence that Sascha had been a neo-Nazi, a political stance that apparently inspired him in 2013 to post paranoid videos in which he accused Muslims of trying to implement Sharia in Germany.

Yet German authorities believe a year later he converted to a fundamentalist branch of Islam and had since been spreading symbols of the Islamic State online.

Matthias Quent ― director of the Thuringian Center for Documentation and Research Against Group Focused Enmity at the Institute for Democracy and Civil Society in Germany – explained that “on one hand, the hate groups of the far right need the Islamist terrorism to scapegoat Muslims and to legitimize their law-and-order ideology.”

But on the other hand, he said, neo-Nazis and radical Islamists share one major “ideological link”: anti-Semitism.

He pointed to how members of the far-right in Germany, along with racist figures in the U.S. like David Duke, attended a 2006 Holocaust denial conference in Iran hosted by that country’s former extremist president, Mahmoud Ahmadinejad.

There are also many German neo-Nazis, Quent said, who often express “sympathy” for “the unscrupulousness and the will of the islamists and their anti-Semitism and anti-Americanism.”

This is true in the U.S. as well. In a recent Atlantic profile of Richard Spencer, the American white supremacist troll, Spencer speaks admiringly of ISIS, calling it an “identify movement” and a “grassroots movement” with its own “ideas.”

“They’ve built themselves up fast, from nothing,” Spencer said.

Joshua Roberts/Reuters Richard Spencer, an American white supremacist, has spoken admiringly of ISIS.

However according to Levin, the California State professor, the most unifying characteristic between neo-Nazis and Salafist jihadis might be psychological.

“The bottom line is this: Extremism does not attract the most stable of people,” he said. “Much of the appeal of extremist ideology is not only based on doctrine but on the kind of empowerment it yields to the follower.”

“And sometimes,” he said, as in the case of Arthurs, “you trade in one kind of extremism for another.”

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