Police said they were looking into the possibility of a hate crime, but that the incident appeared to be triggered by a dispute between neighbors over parking.
The shooter, identified as 46-year-old Craig Stephen Hicks, was being held without bond in the Durham County Jail on three counts of first-degree murder, police said.
The victims, who were pronounced dead on the scene, were identified as Chapel Hill residents Deah Shaddy Barakat, 23, and his wife Yusor Mohammad, 21, as well as her sister Razan Mohammad Abu-Salha, 19, of Raleigh.
Hicks turned himself in after the shooting Tuesday in Chapel Hill, just outside the campus of the University of North Carolina.
“Our preliminary investigation indicates that the crime was motivated by an ongoing neighbor dispute over parking,” Chapel Hill police said in a statement, adding that Hicks was cooperating with investigators.
“Our investigators are exploring what could have motivated Mr Hicks to commit such a senseless and tragic act. 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,” Police Chief Chris Blue said.
A Facebook page believed to belong to Hicks showed dozens of anti-religious posts, including one calling himself an “anti-theist,” saying he has a “conscientious objection to religion,” and other memes denouncing Christianity, Mormonism and Islam.
His page also showed a photo of a loaded revolver, alongside a video of a puppy and a promotional clip for Air New Zealand.
One post read: “I’m not an atheist because I’m ignorant of the reality of religious scripture. I’m an atheist because religious scripture is ignorant of reality.”
“Given the enormous harm that your religion has done in this world, I’d say that I have not only a right, but a duty, to insult it,” he posted under the religious beliefs tab.
Reaction to shooting lit up Twitter, with one of the top trending hashtags being #MuslimLivesMatter – a parallel to the “Black Lives Matter” movement sparked by police killings of African Americans in recent months.
Photos of the three victims circulated on social media, including recent wedding pictures of Barakat and his wife.
Reports said Barakat was a second-year student in dentistry there, while Mohammad was planning to begin her dental studies in the fall.
Abu-Salha was a student at North Carolina State University, according to the UNC university newspaper, the Daily Tar Heel.
A Facebook community –– Our Three Winners –- has been set up for posts about the three students.
“Deah Barakat, Yusor Abu-Salha and Razan Abu-Salha have returned to their Lord,” the site’s creators state. “They have set an example in life and in death.”
The site features a photo of the three smiling at what appears to be graduation ceremony. The women wear Muslim head scarfs, one of them also in a blue graduation cap.
Barakat’s brother Farris mourned the deaths, writing “it doesn’t make sense” on his own Facebook page.
“Please pray for them, their friends, and the family. I haven’t even begun to fully comprehend what has happened. But I know for sure those three together have done so much we are all proud of,” Farris Barakat wrote.