警方表示，一輛深色奧迪A4 Avant BB的司機可能有與案件相關的信息。
它說，在Barton Place的Sainsbury's和ASDA Belmont Road之間，有人看到這輛車在Bagley先生被刺傷的當晚22:37至22:50之間行駛。
Det Ch Insp Harding說，他的團隊在查看了數小時的閉路電視錄像後發現了這輛車。
Murder police investigating an unsolved stabbing want to speak to an Audi driver who could be a witness.
West Mercia Police said Christian Bagley, 30, was stabbed twice as he walked under the Hunderton Bridge in Hereford on Father's Day, 21 June 2015.
The force said the driver of a dark Audi A4 Avant BB might have information relevant to the case.
It said the car was seen driving between Sainsbury's at Barton Place and ASDA Belmont Road between 22:37 and 22:50 BST on the night of Mr Bagley's stabbing.
Det Ch Insp Harding said the car had been spotted after his team viewed hours of CCTV footage.
He said the male driver was seen getting out of the car near the entrance to ASDA and speaking to another person briefly, before returning to the vehicle and leaving.
The driver was not a suspect, he stressed, but "may be a key witness".
He added he recognised the "passage of time presents difficulties for people being able to remember where they were and what they were doing", but hoped the appeal, on the seventh anniversary of Mr Bagley's death, would trigger someone's memory.