Mr Kettule, 34, was found fatally shot in the driveway of a Ware Street home in Fairfield, at about 2.40am on January 10.
Later that day, a dark-coloured Jeep Cherokee – believed to be used in the shooting – was found burnt-out at Reserve Street in Smithfield.
Detectives have now released further CCTV vision of two men seen in the vicinity of Ware Street around the time of the shooting.
The men in the vision are wearing black pants and black hooded jackets.
One of the men appears to have a face covering and is wearing dark-coloured shoes.
The other man is wearing white sneakers.
Detectives have also released CCTV vision of a white Toyota Corolla hatchback which was seen in Reserve Street at Smithfield about 8.15pm the same day.
“We believe the hatchback was used to pick up the men in Reserve Street after the Jeep Cherokee was abandoned and burnt-out after the murder,” Homicide Squad Commander Detective Superintendent Danny Doherty said.
“This violent, brazen attack was carried out in the driveway of a suburban home, and I implore the public to come forward to police and help us identify those responsible.”