CHAPEL HILL, N.C. — On the last day of Razan Mohammad Abu-Salha’s life, it was too cold to run.

Ms. Abu-Salha, a 19-year-old North Carolina State University sophomore, was training with a friend for a half-marathon in Raleigh. But when her design class let out after noon that Tuesday, Feb. 10, the wind chill was 30 degrees — painful for a North Carolinian. Instead, she hopped into her red Toyota Corolla and set off on the 25-mile drive to the Chapel Hill condominium where her newlywed sister, Yusor Mohammad Abu-Salha, had recently moved in with her husband, Deah Shaddy Barakat.

That evening, at 5:11, a woman who had just gotten off the bus near the condominium complex heard gunshots and screams and called 911. The Chapel Hill police arrived to find Mr. Barakat, 23, dead beside his front door, bleeding from the head. Yusor, 21, and Razan lay lifeless in the kitchen. An hour later, their neighbor Craig Stephen Hicks, 46, turned himself in to the sheriff’s office in Pittsboro, 20 miles south.

Since then, in the absence of hard facts about Mr. Hicks’s motives, two competing narratives have emerged. The first, which spread almost instantly around the world on social media, was that the shootings were an anti-Muslim hate crime.

Mr. Hicks’s wife, Karen Haggerty Hicks, suggested another motive. The killings, she said at a news conference the next day, had nothing to do with the victims’ faith, but were “related to a longstanding parking dispute that my husband had with the neighbors.”