Two men and a woman have been arrested as part of murder inquiry into the death of Fahad Mohamed Nur near Cathays Railway Station.
The men, aged 24 and 22, from Cardiff, have both been arrested on suspicion of murder.
A 34-year-old woman from Birmingham has been arrested on suspicion of assisting an offender.
Police say the younger male and the woman were arrested at Heathrow Airport early this morning and will be brought back to Cardiff for questioning.
Officers were called to the lane which links Park Place to Corbett Road at approximately 00:24hrs on Sunday, June 2 following reports that a man had been stabbed.
The 18-year-old victim was taken to the University Hospital of Wales, Cardiff, where he died from his injuries.
South Wales Police said they were grateful to the community for their support in the investigation and they continue to appeal for witnesses.
Police say the CCTV footage shows there were several potential witnesses in the area and are also appealing for any dashcam footage from passing vehicles.