Muslim anger and frustration rose here Thursday, an emotional day when three young American Muslims were buried after being shot to death, allegedly by a white neighbor who had publicly railed against religion.

At a solemn outdoor funeral attended by several thousand people, Mohammad Abu-Salha, the father of two of the murder victims, called for a federal investigation into the case, which he said “has ‘hate crime’ written all over it.”

The FBI said Thursday evening it had opened “a parallel preliminary inquiry to determine whether or not any federal laws were violated.”

Police have said their initial investigation suggested that Craig Hicks, 46, shot the three university students to death Tuesday because of a long-running dispute over parking at their condominium complex in Chapel Hill, close to the campus of the University of North Carolina. Hicks has been charged with three counts of murder.

University, local and religious leaders have publicly cautioned against jumping to conclusions about whether the victims’ faith in some way triggered the lethal outburst.

But Thursday’s outpouring of grief for the three young people, hailed as beloved volunteers and mentors in the area’s large Muslim community, seemed to move more and more people to openly assert that whether the motivation was religion or not, anti-Islamic sentiment is a deep and painful problem that American Muslims confront daily.

“It’s really hard to believe that it wasn’t induced by some sort of racism toward them,” said Imam Adeel Zeb, Muslim chaplain at Duke University.

Zeb said the national response to the deaths of Deah Barakat, 23, and Yusor Mohammad Abu-Salha, 21, a married couple, and Abu-Salha’s sister Razan, 19, highlights the “double-standard” that exists in the United States.

He said that if a Muslim had killed three non-Muslims, the news coverage and public discussion of the case would be vastly different.

“Any time an incident happens and it’s done by a Muslim, it has to be because of Islam,” Zeb said. “But if it’s somebody else, it must be because of mental illness, or something else, like an argument over parking spaces. There is a double standard, and it makes you feel like a second-class citizen.”

Imran Aukhil, 30, a close friend of Barakat’s family, was for nearly a decade the spokesman for the Islamic Association of Raleigh, where Thursday’s funeral took place. Born and raised in North Carolina and a longtime member of the mosque’s governing board, he recently moved to New York to work for a consulting firm but flew to North Carolina when he heard the news.

Aukhil said he believed the problem in America was greater than anti-Muslim bias; he said the issue was how all U.S. minorities are treated in a culture of “white privilege.”

“The greatest threat in America is frankly white men with grudges and guns,” he said at local coffee shop just before the funeral.

Aukhil said he understood that his language was inflammatory and would anger some people. He said he was speaking bluntly because he was emotional, angry and grieving the loss of three “charitable, loving, kind and generous” friends — and was frustrated by anti-Muslim sentiment in America that he says has been growing since 9/11.

“You would think that the way politicians and media outlets talk about it, that Muslims are lurking right around the corner waiting to kill anybody and everybody,” he said. “But that is not the case at all. The reality is deranged people, many of whom are white, many of whom are proud Americans with flags all over their cars and their homes, they are the greatest danger to America.

“They are the ones who are committing some of the most atrocious crimes — the Aurora, Colorado, shooting, the Connecticut shooting, how many mass murders committed by white males can we list? That unfortunately is completely misrepresented by the media, who say that Islam and Muslims are going to come and destroy America.”

Imam Abdullah Antepli, a top Duke University Islamic leader, noted at a news conference Wednesday evening that many Muslim families had kept their children home from school Wednesday because they were worried for their safety.

“The sense of alienation, the sense of vulnerability, I cannot describe,” Antepli said.

While cautioning that it was too soon to judge whether the shooting was a hate crime, he said Muslim Americans had already been feeling rising tensions, due in part to the rise of the Islamic State in Iraq and Syria.

It is “absolutely the case that rising anti-Islam and anti-Muslim sentiment in American society has revealed its ugliest face over this case,” he said. “But I think dwelling on this will only add layers of pain to the families of these three wonderful individuals.”

At the funeral, which was held on an athletic field across the street from the mosque to accommodate the huge crowd, most of the focus was on remembering Barakat, who was studying dentistry at UNC; his wife, Yusor, who was scheduled to start in the same program in the summer; and Razan, a design student at North Carolina State University.

Abu-Salha called his younger daughter “the breeze of the day — she walked on this Earth lighter than air.”

In interviews, people who attended the funeral recalled Barakat’s charitable work. He passed out free dental supplies to the homeless in Raleigh and Durham and was planning a trip to Turkey this summer to distribute dental supplies to Syrian refugees there. His wife, whom he married in December, made a similar trip to refugee camps in Turkey last year.

The three have been remembered in moving candlelight vigils Wednesday night at UNC and Thursday evening at N.C. State. They were buried Thursday in simple plots in an Islamic cemetery in the North Carolina countryside.

Amid the tributes and farewells, people discussed whether bias against Muslims may have played a part in the shooting. Many said it was premature to judge before the police finish their investigation. But others said that Abu-Salha was right when he said that hate clearly motivated the “execution-style” murders.

“It was not about a parking spot,” Abu-Salha said, calling on President Obama to order a federal investigation.

Abu-Salha and others have pointed to Hicks’s Facebook postings, in which he professed his atheism and condemned all religions.

Hicks’s wife and her attorney have both denied that the shootings were motivated by the victims’ religion.

“What’s the difference between Charlie Hebdo and what happened here?” asked Molham al-Hasni, referring to the deadly recent attacks in Paris on a satirical newspaper by radical Islamist militants.

“In Charlie Hebdo, all the presidents of the world went into the streets to march,” Hasni, who said he came to the United States from Syria three years ago, said at the funeral. “When we see a Muslim killer, we say ‘terrorist,’ but if he’s white, we say he’s crazy. It’s not fair.”

Hasni said he was granted asylum in the United States because he was a human rights activist in Syria and feared for his life in the war raging there. He said he is grateful to America for helping him and “saving my life,” but he still believes that many Americans have a bias against Muslims.

“There is no other country in the world that gives Muslims as much freedom and support and kindness as America, broadly speaking,” Aukhil said. “But the underlying bias and injustice that Muslims have been subject to for the last couple of decades” is “really starting to get frustrating.”

Aukhil said the huge crowds at the vigils and the national outpouring of support for the victims was heartening.

“If there is a silver lining to this, I feel like the tide is changing,” he said. “I feel like this has shaken the entire nation, the loss of these three incredibly beautiful people, these innocent people who were beloved by every single person they touched.”