Police say they are making "significant progress" in their hunt for the killer of Enayit Khalili, but have appealed for more help.
Mr Khalili was fatally stabbed at about 3.30am on Saturday, March 24, in Fiennes Road, Rose Hill, Oxford.
Today, Det Chief Insp Joe Kidman made a second appeal for a young woman who was seen talking on her mobile phone near a telephone box in Ashurst Way, near the junction of Fiennes Road, to come forward.
He said: "We have not yet identifed any witnesses to the actual attack. We have had a number of reports of a young woman talking on a mobile phone near the telephone box.
"She was there at least 20 minutes and probably longer. She may well have vital information for this inquiry."
A forensic examination of the scene has so far failed to provide a breakthrough.
However, Mr Kidman said that a large number of fingerprints were taken from Mr Khalili's house.
He added: "Significant progress has been made. However, this remains a challenging inquiry."
Mr Khalili's family in the UK returned to Afghanistan for his funeral several weeks ago and his wife, mother and brothers are now in a period of mourning.
Anyone with information is asked to call police on 08458 505505 or Crimestoppers anonymously on 0800 555111.