It follows the death of 29-year-old Patrick Bradley, from Greenock, who was found seriously injured in Wellington Street in the town in the early hours of Friday, August 30.
Three people have since appeared in court charged with murder following Mr Bradley's death.
Police Scotland said following extensive inquiries a Major Investigation Team is now appealing for three people, two men and a woman, who they believe may have been witnesses to come forward.
Officers believe the two men were possibly walking with a medium sized dog in Wellington Street near Wellington Path around the time of the disturbance.
The woman is described as wearing light clothing and had light blonde hair which was tied back in a loose ponytail. Detective Inspector Una Maider, who is leading the investigation, said: "Firstly I would like to reiterate that we are looking to identify these three people as witnesses to the disturbance.
"I would ask anyone either who lives locally in the area or taxi drivers or motorists who may have been around the Wellington Street area to contact me."
Ccontact me at Greenock Police office on 01475 492500, the non emergency number 101, or via CRIMESTOPPERS on 0800 555 111.
Three men aged 16, 19 and 37 have been arrested and charged with murder in connection with the incident.
Derek Paterson or Grant, 37, from Glasgow, appeared at Greenock Sheriff Court along with Jordan Grant, 19, and Lee Grant, 16, both from Greenock, on Wednesday, September 4.
All three men made no plea or declaration and were remanded in custody.