Emergency services were called to a home in Heddon Greta, about 20km east of the small town of Cessnock, with reports of the shooting on December 27.
Zachery 'Zac' Davies-Scott, 25, was given first aid but died at the scene.
Strike Force Roslyn was formed to investigate the shooting, with members of the Homicide Squad, and local police.
A number of people allegedly tried to force their way into the Heddon Greta home before Mr Davies-Scott was shot, police have been told.
The group then fled the scene in a white SUV, which was seen travelling on nearby Main Rd shortly after the shooting.
Police seized a white 2015 Mitsubishi Outlander from Newcastle in February this year, and on Wednesday released CCTV showing a man at a service station in Lambton.
The man is Caucasian, of a solid build with dark hair and was wearing a black T-shirt with a white Nike logo, black shorts, white shoes, a baseball cap and a cross-body bag.
Anyone who recognises the man, or has any information linked to the shooting is urged to come forward immediately, Homicide Squad Commander Detective Acting Superintendent Virginia Gorman said.
"We believe someone must know something, and no piece of information is too small," he said.
"Our detectives are examining every piece of CCTV, looking at every clue, and following every lead.
"We will not stop until we have brought those responsible for Zac's death to justice."
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