RALEIGH, N.C. (AP) — The fathers of three young Muslims allegedly slain by a neighbor who was angry over parking spots stood before their caskets Thursday and urged a crowd of thousands to protect others by demanding justice.

More than 5,000 people came to the funeral of Deah Shaddy Barakat, 23; his wife, Yusor Mohammad Abu-Salha, 21; and her sister Razan Mohammad Abu-Salha, 19, who were killed Tuesday in the couple’s Chapel Hill apartment.

A self-described “gun toting” atheist with a reputation for bullying his neighbors, Craig Stephen Hicks, turned himself in and was jailed on first-degree murder charges.

Chapel Hill police said they are investigating whether religious or ethnic hatred motivated Hicks in any way, and federal investigators said hate crimes haven’t been ruled out. The FBI also announced Thursday that it has “opened a parallel preliminary inquiry to determine whether any federal laws were violated.”

U.S. Attorney Ripley Rand, the district’s top federal prosecutor, had said Wednesday that there was no immediate evidence Muslims were being targeted.

And that didn’t sit well with many at the funeral, where the victims were hailed as martyrs for their faith.

“When we say this was a hate crime it is all about protecting all other children in the USA,” Dr. Mohammad Yousif Abu-Salha, who lost his daughters, told the crowd. “It’s all about making this country that they loved, where they lived and died, peaceful for everybody else.”

“We need to identify things the way they really are,” Abu-Salha continued. “If somebody picks up a fight about anything they can invent, and they murder three people execution-style, we know what this is about. And they have posted on their Facebook how much they hated faith, there’s no doubt.”

The funeral crowd was so large it had to be moved from a mosque to an athletic field at North Carolina State University in Raleigh, where all three studied before Barakat and Mohammad moved to Chapel Hill to pursue careers in dentistry.

The families viewed the victims’ bodies in a small building before the funeral. Then midday Muslim prayers were held. The crowd was solemn and silent — only a few children crying in the distance could be heard. Finally, hearses carried the three coffins, in gray, white and silver, to an Islamic cemetery outside Raleigh.

Namee Barakat told the AP that Hicks had visited his son’s condo before, flashing his gun as he demanded they stop using visitors’ parking spots.

“Yusor told her dad that this guy, he does not like us,” Barakat said. “He does not like our hijab. She was concerned.”

Abu-Salha told the AP that he’s certain his daughters “were targeted for their religion.”

“This is not a parking dispute,” he said. “These children were executed with shots in the back of the head.”

Police have said they are not commenting on evidence in the case, including manner of death.

“We understand the concerns about the possibility that this was hate-motivated, and we will exhaust every lead to determine if that is the case,” Chapel Hill police Chief Chris Blue said in an email Wednesday.

Hicks, 46, is a Second Amendment rights advocate with a concealed weapons permit who often complained about organized religion on Facebook. “Some call me a gun toting Liberal, others call me an open-minded Conservative,” Hicks wrote.

Neighbors described him as angry and confrontational; His ex-wife told the AP that he was obsessed with the 1993 shooting-rampage movie “Falling Down,” and showed “no compassion at all.” His current wife said she believes the killings “had nothing do with religion or the victims’ faith.” She then announced that she’s divorcing him.

The couple met while helping to run the Muslim Student Association at N.C. State, before Barakat moved to Chapel Hill to study dentistry at UNC. Yusor Abu-Salha, who graduated in December, planned to enroll in the dental school in the fall. Razan Abu-Salha, still at N.C. State, was visiting from Raleigh when they were killed.

Family and friends remembered them as outgoing and optimistic young adults working to make the world a better place. The newlyweds had planned to travel to Rihaniya, Turkey, this summer to provide free dental care for Syrian refugee schoolchildren. To offset the costs, Barakat posted a video on a fundraising website seeking $20,000 in donations. Contributions surged after their deaths, to more than $250,000 by Thursday.

Barakat’s family was from Syria, although he was born in the U.S. Yusor Abu-Salha was born in Jordan and came to the U.S. with her family as a young girl. In an interview recorded last year as part of the StoryCorps project and broadcast by North Carolina Public Radio on Thursday, she expressed gratitude for her adopted homeland.

“Growing up in America has been such a blessing,” she said. “And, you know, although in some ways I do stand out, such as the hijab I wear on my head, the head covering, there’s still so many ways I feel so embedded in the fabric that is our culture. That’s the beautiful thing here, is that I doesn’t matter where you come from. There are so many people from so many different places, of different backgrounds and religions. But here we’re all one – one culture.”