A graduate student at the University of North Carolina at Chapel Hill was charged Tuesday with first-degree murder in the fatal shooting of one of his professors the previous day, in an attack that paralyzed the community for hours as police combed the campus for a gunman on the loose. Campus police confirmed that Tailei Qi, 34, had known his victim, Zijie Yan. Brian James, the UNC chief of police, said that “the suspect went directly to the victim and then left Caudill Labs” on Monday. He was arrested about 90 minutes after the shooting, James said. Qi is listed as one of three graduate students in a research group overseen by Yan, according to the group’s website, which states that Qi joined the group last January. He also appears to have authored at least two research papers with Yan, who was elsewhere named as his adviser, according to the Associated Press. James declined to speculate on a motive on Tuesday, but said that having arrested Qi alive was an advantage to investigators. “To actually have the suspect in custody gives us an opportunity to figure out the why and even the how, and also helps us to uncover a motive and really just why this happened today,” he said. “Why today, why at all?”