A gunman who had posted anti-religious messages on Facebook and quarreled with neighbors was charged with killing three young Muslims in what police said on Wednesday was a dispute over parking and possibly a hate crime.

Craig Stephen Hicks, 46, a full-time paralegal student from Chapel Hill, was charged with first-degree murder in Tuesday's shootings around 5 p.m. (2200 GMT) two miles (three km) from the University of North Carolina campus.

The victims were newlyweds Deah Shaddy Barakat, 23, a University of North Carolina dental student, and his wife Yusor Mohammad, 21, and Yusor's sister, Razan Mohammad Abu-Salha, 19.

All were involved in humanitarian aid programs.

Students at UNC, where Yusor Mohammad was going to join her husband as a student later this year, gathered on Wednesday for an evening vigil and prayer service.

The suspect, in handcuffs and orange jail garb, appeared briefly on Wednesday before a Durham County judge who ordered him held without bail pending a March 4 probable cause hearing.

Police said a preliminary investigation showed the motive to be a parking dispute. They said Hicks, who has no criminal history in Chapel Hill, turned himself in and was cooperating.

The killings drew international condemnation. The shooting sparked the hashtag #MuslimLivesMatter on social media with many posters assailing what they called a lack of news coverage.

"I guess that Muslims are only newsworthy when behind the gun, not in front," tweeted a poster who goes by the handle @biebersrivals.

Muslim activists demanded authorities investigate a possible motive of religious hatred.

"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 a statement.

Hundreds of people gathered on the UNC campus Wednesday evening for a candlelight vigil for the victims.

University and city leaders urged inclusiveness during a time of unease, while a brother of one of the victims called for nonviolence.

'Execution-style murders'

The killings occurred in a condominium complex in a wooded area filled with two-story buildings. Neighbors said parking spaces were often a point of contention.

"I have seen and heard (Hicks) be very unfriendly to a lot of people in this community," said Samantha Maness, 25, a community college student. But she said she had never seen him show animosity along religious lines.

On Facebook, Hicks' profile picture reads "Atheists for Equality" and he frequently posted quotes critical of religion. On Jan. 20 he posted a photo of a .38-caliber revolver that he said was loaded and belonged to him.

Hicks' wife, Karen Hicks, told reporters at a news conference that her husband had been locked in a longstanding dispute over parking and the killings had nothing to do with religion. She said Hicks was not hateful and believed "everyone is equal."

Barakat's family urged the shooting be investigated as a hate crime and said the three were killed with shots to the head.

"Today, we are crying tears of unimaginable pain over the execution-style murders," Barakat's older sister Suzanne told reporters. She said her brother was light-hearted and loved basketball.

The incident appeared to be isolated and not part of a targeted campaign against North Carolina Muslims, Ripley Rand, U.S. Attorney for the Middle District of North Carolina, told a news conference with local police officials.

Imam Abdullah Antepli, chief representative of Muslim affairs at Duke University, told the news conference it may or may not have been a hate crime and called for an easing of tensions.

A turning point?

Groups including the Muslim Public Affairs Council, the Council on American-Islamic Relations (CAIR) and the local Raleigh-based Muslims for Social Justice called for a federal investigation into possible hate crimes.

"I hope this terrible tragedy will be a turning point that brings the reality home that if we keep demonizing Muslims and equating their religion to terrorism, it will lead to more attacks," said Manzoor Cheema, co-founder of Muslims for Social Justice.

Barakat, an American citizen of Syrian origin, wrote in his last Facebook post about providing free dental supplies and food to homeless people in downtown Durham. He was raising funds for a trip to Turkey with 10 other dentists to provide free fillings, root canals and oral hygiene instruction to Syrian refugee children.

His sister-in-law, Abu-Salha, a sophomore at nearby North Carolina State University, was involved in making multimedia art to spread positive messages about being Muslim American.

Students at UNC said the three friends came from two of the most prominent Muslim families in the Raleigh area.

"Deah was a very proud Muslim American. He was proud of all his identities," said Sofia Dard, a 21-year-old senior psychology major. She said Muslims were used to occasional harassment in post-9/11 America, but the shooting "adds a whole level of seriousness."