Police arrested 47-year-old Gianluca Ros on suspicion he stabbed two men inside an apartment block in the residential area of Etterstad at around 10pm on Sunday.
The man was caught after police received a tip-off from a member of the public as to his whereabouts. He was arrested at 11.30pm without any problems.
Both the victims were taken to Ullevål hospital in Norway's capital, where the 40-year-old victim died from his injuries. The other man is in a serious condition. Both were Norwegian citizens.