18-year-old Fahad Mohamed Nur died following an incident in a lane near Cathays Railway Station.
Officers were called to a lane adjacent to the railway line which links Park Place to Corbett Road at approximately 00:24hrs on Sunday, June 2 following reports that a man had been stabbed.
Mr Nur, who is from Cardiff, was taken to the University Hospital of Wales, Cardiff, where he died from his injuries.
His family is being supported by specially trained officers.
No further action is being taken against two local men, aged 17 and 18, who were arrested in connection with the incident.
They have been released from police custody.
Officers are appealing for information, believing the area to be busy at the time of the incident.
They would like to speak to anybody who may have witnessed the incident, or who may have seen anything suspicious before or after.
Senior Investigating Officer, Detective Chief Inspector Mark O’Shea, from South Wales Police, said: “A young man has tragically lost his life and we are doing all we can to identify and arrest those responsible for the murder of Fahad Mohamed Nur.
“A police cordon remains in place and we thank the local community for their support and patience while we continue our investigation.
“Cathays is a very busy area and we know there were number of people near the Student’s Union in Park Place and on Corbett Road close to The Woodville pub who may have heard or seen something.
“We would ask anyone with information to please contact us.”
South Wales Police via 101 or Crimestoppers anonymously on 0800 555 111 quoting reference number *198071.