CHAPEL HILL, N.C. (AP) — A long-running parking dispute between neighbors motivated a man to kill a woman, her newlywed husband and her sister at a quiet condominium complex near the University of North Carolina, police said Wednesday.

A Muslim advocacy organization asked authorities to address speculation — much of it on social media — about possible religious bias in Tuesday's shooting of the three Muslims.

"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.

The couple had graduated from North Carolina State, and one was studying to be a dentist at UNC. The sister was an undergraduate at N.C. State. UNC's chancellor called it a loss for both campus communities, and the school planned a vigil Wednesday evening.

"This was like the power couple of our community," said Ali Sajjad, president of N.C. State's Muslim Student Association.

Craig Stephen Hicks, 46, was charged with three counts of first-degree murder in the shooting of Deah Shaddy Barakat, 23, and wife Yusor Mohammad, 21, both of Chapel Hill, and Razan Mohammad Abu-Salha, 19, of Raleigh.

Hicks appeared briefly in court Wednesday. He is being held without bond and will be appointed a public defender. A probable cause hearing is scheduled for March 4.

Police said Hicks turned himself in and was cooperating. They said the preliminary investigation showed the parking dispute was the motive.

Hicks' wife, Karen Hicks, and a former roommate of Barakat confirmed that Craig Hicks had been part of a long-running parking dispute.

"I can say that it is my absolute belief that this incident had nothing up do with religion or the victims' faith, but in fact was related to long-standing parking disputes my husband had with various neighbors regardless of their race, religion or creed," Karen Hicks said.

One of her attorneys, Robert Maitland, said Hicks had tried to resolve the parking dispute with the homeowners association several times without success.

Imad Ahmad, who said he lived with Barakat for more than a year, said Hicks would knock on their door about once a month to complain the two men were parking in one of the spaces designated for visitors in addition to the one space reserved for each residence.

"He would come over to the door. Knock on the door and then have a gun on his hip saying you guys need to not park here," said Ahmad, 24, who said Hicks carried the handgun in a holster. "He did it again after they got married."

Another attorney for Karen Hicks, Michele English, said Craig Hicks had a concealed weapons permit.

But outrage spread among some American Muslims who viewed the homicides as an outgrowth of anti-Muslim opinions. Many posted social media updates with the hashtags #MuslimLivesMatter and #CallItTerrorism.

"Based on the brutal nature of this crime ... the religious attire of two of the victims, and the rising anti-Muslim rhetoric in American society, we urge state and federal law enforcement authorities to quickly address speculation of a possible bias motive in this case," Nihad Awad, of the Council on American-Islamic Relations, said in a statement.

Durham district attorney Roger Echols said he couldn't discuss motive or whether Hicks could be charged with a hate crime.

U.S. Attorney Ripley Rand said his office was monitoring the investigation but that it was not yet a federal investigation. He said the shooting appeared to be "an isolated incident."

Gerod King of the Bureau of Alcohol, Tobacco, Firearms and Explosives said that agents were in touch with the U.S. attorney's office and that investigators hadn't ruled out a hate crime.

At UNC, Barakat was a second-year dental student. Mohammad was scheduled to begin dental studies in the fall.

Both graduated from North Carolina State University, spokesman Mick Kulikowski said. Barakat received a business administration degree in 2013. Mohammad received a biological sciences degree in December.

Abu-Salha was a sophomore design major, Kulikowski said.

Muneeb Mustafa, 23, of Cary, said he attended the same Raleigh mosque as Barakat.

"He was a completely genuine guy. Loving, caring, friendly, smart," Mustafa said. "He was an ideal human being. He was a role model."

Mustafa said they last saw each other about a month ago, playing in a basketball tournament staged by the Muslim Student Association at UNC, Mustafa said. Barakat, his wife of less than two months and his sister were Muslim, Mustafa said.

Barakat's family was from Syria, and he raised money to help refugees, Mustafa said. Mohammad traveled to Turkey last summer to help treat refugees' dental problems, Mustafa said.

The neighborhood where the victims were found — about three miles east of campus — consists mostly of apartments and condominiums rented by students. Residents said they'd never before seen police or had crime problems.

"It's a very quiet community," resident Bethany Boring told WRAL-TV. "It's a lot of graduate and professional students. You know, professional families."

Shadi Wehbe, a UNC graduate who has lived in the complex since 1999, said that two weeks ago, a woman came to his door about 10 p.m. and politely asked him to move his car. Some parking spots are assigned, and others are open. Wehbe said parking had never been a problem and no one had asked him to move his car before, but he realized he was in the wrong spot and moved his car one place over.

Neighbor Samantha Maness said suspect Hicks "complained about noise and parking. So I wasn't extremely surprised" when he was charged.

"Anytime that I saw him or saw interaction with him or friends or anyone in the parking lot or myself, he was angry," she said. "He was very angry, anytime I saw him."

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Associated Press writers Allen G. Breed in Chapel Hill, Jonathan Drew in Durham, Emery Dalesio in Raleigh and Eric Tucker in Washington contributed to this report.