A University of North Carolina graduate student walked into a classroom building, shot his faculty adviser and quickly left, authorities said a day after the attack paralyzed campus as police searched for the gunman.

Tailei Qi, 34, was charged Tuesday with first-degree murder and having a gun on educational property in Monday’s killing of Zijie Yan inside a science building at the state’s flagship public university.

Chapel Hill police arrested Qi without force in a residential neighborhood near campus within two hours of the attack, UNC Police Chief Brian James said at a news conference.

Investigators were trying to determine a motive and searching for the gun, James said. He declined to specify where in Caudill Labs Yan was killed, saying officers are still looking at evidence. Qi was already gone when a team of officers reached the building, James said.

On Wednesday afternoon, the school’s iconic Bell Tower will ring in honor of Yan’s memory and students are encouraged to take a moment of silence, he said. The school also canceled classes until Thursday.