Correction: An earlier version of this story included a quote from Richard Dawkins that was wrongly attributed to Hicks. This version has been corrected.

The alleged assassination by an outspoken North Carolina atheist of three of his Muslim neighbors is shining a light on particular, deep tensions between two tiny American groups: Muslims and atheists.

Police in Chapel Hill Wednesday said they are only at the start of their probe into Craig Hicks’ life and what led up to Tuesday night, when he allegedly shot and killed husband and wife Deah Barakat, 23, and Yusor Mohammad, 21, and Mohammad’s sister Razan Mohammad Abu-Salha. They said initial reports indicated that there was a dispute about parking but that their investigation continues.

Police arrested Hicks, 46, and charged him with the shootings. Hicks turned himself in “without incident” to the Chatham County Sheriff’s Office in nearby Pittsboro, Chatham County Sgt. Kevin Carey said Wednesday.

On Wednesday, the father of the two women said one of his daughters had mentioned Hicks’ before and felt he was anti-Muslim. A week ago, he said, she told her family she had  “a hateful neighbor.”

“Honest to God, she said, ‘He hates us for what we are and how we look,’” Dr. Mohammad Abu-Salha, who has a psychiatry practice near Chapel Hill, told The News Observer.

Later on Wednesday, Hicks’s wife insisted that the shooting was only due to parking arguments and not to any bigotry. “I can say with my absolute belief that this incident had nothing to do with religion or victims faith, but in fact was related to the long-standing parking disputes that my husband had with the neighbors. ” Karen Hicks said during a news conference.

But reports that an outspoken atheist — most of Hicks’ many Facebook posts railed against religion — had attacked a family who were visibly Muslim (the women wore headscarves) tapped immediately into a conversation that has been going on since Sept. 11 about why several of atheism’s biggest figures have singled out Islam for criticism.

Among them are biologist and writer Richard Dawkins and neuroscientist Sam Harris, who have both triggered controversy with their comments about Islam.

For example, after the Paris attacks on magazine Charlie Hebdo, Dawkins tweeted that “all religions are NOT equally violent. Some have never been violent, some gave it up centuries ago. One religion conspicuously didn’t.”

In an essay around the time of the controversy about a proposal to build a mosque near Ground Zero, Harris wrote that “At this point in human history, Islam simply is different from other faiths,” and that terrorist groups like al-Qaeda and the Taliban aren’t veering from the basic faith. “If they are ‘extremists’ who have deformed an ancient faith into a death cult, they haven’t deformed it by much. When one reads the Koran and the hadith, and consults the opinions of Muslim jurists over the centuries, one discovers that killing apostates, treating women like livestock, and waging jihad—not merely as an inner, spiritual struggle but as holy war against infidels—are practices that are central to the faith.”

The tensions have been central enough that umbrella secular and atheist groups Wednesday were quick to release statements condemning the Chapel Hill killings. Ron Lindsay, president of the skeptics’ group Center for Inquiry said atheists have in the past held conferences on the topic of Islam and tried to “reach out for dialogue” but the overtures have been viewed skeptically by Muslims.

Lindsay and other secular groups said Wednesday that the atheists’ particular focus on Islam has been triggered by the comments of big-name celebrities like Harris.

“I don’t think he’s an Islamophobe. But it’s fair to say in his writings that he portrays Islam as inherently more violent-prone than other religions and that has had an effect on some people, maybe an unintended affect. A lot of people tend to see Muslims in their mind are more of a threat and tend to lump Muslims together,” Lindsay said. “To try and put things in focus, clearly we’re concerned about Islamic extremism, but we always make this clear, this is a small minority of Muslims.”

Whether Hicks’ had a particular focus on Islam isn’t clear. Among his hundreds of likes on Facebook are Harris and Dawkins, but his many anti-religion posts span focus from Islam to Christianity to Mormonism.

“My respect for the Abrahamic religions went up in the smoke and choking dust of September 11th. The last vestige of respect for the taboo disappeared as I watched the ‘Day of Prayer’ in Washington Cathedral, where people of mutually incompatible faiths united in homage to the very force that caused the problem in the first place: religion,” he wrote in 2012, quoting Dawkins.

He also writes about what he characterizes as the importance of personal responsibility — even in the case of religion.

“I guess after the horrible tragedy early this week in Arizona, all Glock pistols will officially be labeled “assault weapons.” While I never cared for Glocks personally, it stinks that anyone would blame a firearm rather than the operator of such firearm for such a terrible act. I think I’ll start blaming McDonalds for my weight problem, Christianity for the Ku Klux Klan, and Islam for terrorism,”  he wrote in 2011, referencing the shooting of then-C0ngresswoman Gabrielle Giffords at a public event near Tucson.

His posts slamming religion as a force for bad in the world are mixed with photos, including of his weighing his gun on a scale and cutesy animal videos. He complains about other examples of where he sees government intrusion into people’s  ability to exercise their individual rights, and posts often for LGBT rights and the right to abortion.

Jacques Berlinerblau, a Georgetown University sociologist and atheist who writes on secularism, said he was appalled by the Chapel Hill attacks and that they remind him of those against Jews in Paris recently — “the picking out of someone based on their physical attributes, their clothes, their religious markers and murdering them.”

The Chapel Hill killings will be thought-provoking for  American atheists, he said.

“A big kind-of  talking point in the atheist world view is ‘we don’t do the violence thing’” – that it’s a point of pride, he said. However, this case, he said, combined with the Charlie Hebdo attacks require people to think about the connection between public criticism and violence.

Hicks “is receiving messages about organized religions’ shortcomings and translating these message through the lens of mental illness. So it’s unfair to blame normally ordinarily peaceful American atheists for any of this. But we keep returning to this one question about the relationship between critical forms of speech aimed at groups and the consequences they have on minds that are not completely stable…That’s the question it raises again.”

Sam Harris offered an email response to questions about his comments on Islam. The Post agreed to his request to publish it in full: “There is a huge difference between legitimate criticism of bad ideas and bigotry against specific groups of people (which, in the worst case, can result in hate crimes). It is one thing to believe that specific doctrines within Islam (or any system of thought) are unfounded, harmful, and in need of public criticism; it is another thing entirely to hate Muslims (or Arabs, immigrants, etc.) as people.

For instance, I am currently writing a book with a Muslim friend, Maajid Nawaz, who I consider a true hero (Islam and the Future of Tolerance). In this book, I tell Maajid why I think many of the doctrines of Islam are dangerous and irredeemable, while he argues that the tradition has found ways to circumvent the very issues I raise. The result isn’t bigotry; it isn’t even socially awkward. We are simply two friends having a civil conversation on a very important topic.

If a person considers his atheism (a lack of belief in God) or secularism (a commitment to keeping religion out of public policy) a basis for hating whole groups of people, he is either deeply confused about what it means to think critically or suffering from some psychological disorder.”

Meanwhile, a group of atheists is raising money to donate to a cause championed by one of the Muslim victims. Barakat, whose family was from Syria, had started a crowd-sourcing campaign to collect donations for the Syrian American Medical Society Foundation. His “Refugee Smiles,” focuses on providing dental care to refugees of the Syrian War in Turkey.

“There are conflicting reports about what the motivation was,” said Dale McGowan, executive director of the humanist nonprofit, Foundation Beyond Belief, a national organization based in Atlanta. “It doesn’t matter. It’s someone who identified with our community. We need to make a strong statement against the act.”

The non-profit group, which has 2,000 members, has raised more than $100,000 for religious charities in recent years, McGowan said, though the organization vets donations to make sure the money raised doesn’t go to proselytizing.

Sarah Pulliam Bailey contributed to this report.