Officers are making a direct appeal to potential witnesses who may have vital information about the death of off-duty officer PC Gareth Francis.
Detectives have now issued CCTV images of a parked car just a couple of metres away from where the fatal blow was struck.
Police were called to a report of an assault near to the Sir Robert Peel pub on Castle Street in Edgeley, on January 20th 2013.
Emergency services attended the scene within minutes and discovered 28-year-old Gareth with a serious head injury.
Paramedics gave him treatment at the scene and he was taken by ambulance to Stepping Hill Hospital. He sadly died a short time later.
A post mortem examination concluded Gareth died from a head injury following a single punch.
Officers have now released images of a silver Ford Mondeo that was parked on Castle Street at the time of the incident.
A male passenger was inside the nearby Sir Robert Peel pub at the time, but the woman driver was sitting in the car, which was parked just two or three metres from where the incident happened.
Officers have not yet spoken to her and believe she could hold vital information.
Anyone with information can contact either the Major Incident Team on 0161 856 9283, Greater Manchester Police on 101 or Crimestoppers anonymously on 0800 555 111.