Detectives last night quizzed revellers near the Birmingham nightspot where a 23-year-old surveyor was killed.
Paul Tanner was stabbed to death after he handed over his wallet to a gang of teenage robbers near St Paul's Church in the Jewellery Quarter, in the early hours of Friday, March 4.
Mr Tanner, who lived in nearby Hockley, was returning from a night out.
At least six plain-clothed and 12 uniformed police officers revisited the murder scene and nearby bars, restaurants and nightclubs to talk to witnesses.
Detective Inspector John Pyke, who is leading the murder inquiry, said: "Some of those out could have been there on the night Paul was killed.
"We are pursuing several lines of inquiry and our investigation is progressing well, but we want to speak to new witnesses.
"Paul's tragic murder has grabbed the attention of the public, but I feel sure there are people who know the identity of Paul's killers and are reluctant to tell us.
"I appeal to their consciences. There is no reason why this innocent man was stabbed. He clearly wasn't involved in any incidents beforehand."
He added that unprovoked murders were extremely rare.
The officers were in the Jewellery Quarter and St Paul's Square exactly a week on from the attack at about
Paul's father John Tanner, aged 53, a chartered surveyor from Blakedown, near Kidderminster, said: "There have always been people who steal.
"But you don't carry a knife, unless you are going to use it. They carried that knife with the sole intention of intimidation and stabbing someone."
Four youths were arrested in connection with Mr Tanner's death but were later released.
The stabbing is being linked to another street robbery in nearby Caroline Street 10 minutes earlier.
Anyone with information can call police on 0845 113 5000 or the incident room on 0121 626 4017.