The man arrested is in his forties, police say. A warrant had earlier been put out for his arrest.
Deniz, 40, was attacked on December 11th and died in hospital of his injuries two days later. The attack took place inside a university building, but there were no witnesses to the stabbing. A number of people saw a man believed to be the killer running away from the area.
Police in Örebro have been working intensively since the murder to track down the killer. Local police were joined in early January by seven officers from the National Murder Commission (Riksmordkommissionen).
Shortly after the attack a man wearing blood-spattered clothes was seen in a grocery store near the university. The Swedish Forensic Science Laboratory on Tuesday returned enhanced footage from a security camera, believed to show the killer. But police said on Wednesday that the wrong sequence had been enhanced. Another sequence has now been sent for enhancement.
Fuat Deniz moved to Sweden from Turkey with his parents in the 1970s. He was well known among Syrians and Assyrians, and had carried out research on political activists. Colleagues have said they suspect a political motive for the killing. Police say they cannot rule out a political motive and have brought in experts from the Swedish Security Police, Säpo.