A man was seen entering the Coolac Service Centre shortly before the building went up in flames around 10pm on September 5, Strike Force Dosed investigators have revealed.

They returned to the site last week, combing through the debris, and on Monday, November 27, launched a renewed appeal for information.

"Initial inquiries by strike force detectives suggest the fire was deliberately lit, and as part of ongoing inquiries investigators carried out further examination of the scene last week," police said.

"As inquiries continue, police are appealing to speak with anyone who may have information about the incident, including a man who was seen walking into the service station minutes before the fire begun.

"It's believed the man was travelling in a white Toyota Prado.

"Detectives are also appealing to speak to any truck drivers that may have been staying the night at the service station."

Fifty firefighters worked for hours to contain and eventually extinguish the blaze, drawing Rural Fire Service brigades from across the South West Slopes zone and Fire and Rescue NSW support from as far away as Wagga.

They battled exacerbating conditions including gas cylinders and live wires that hindered their ability to launch straight into full firefighting mode on arrival.

Riverina Police District officers declared the premises a crime scene by the following morning, and the investigation is now in the hands of the NSW Police State Crime Command's financial crimes squad arson unit under Strike Force Dosed.

Anyone with information that may assist investigators can make contact by calling Crime Stoppers on 1800 333 000 or using the online reporting page.