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Pullen, 43, died after being hit by a car in the Hunter Region in New South Wales two years ago. He was visiting Australia as a firefighter at the start of the region's bushfire season.
About 5.35am on September 29, 2018, emergency services were called to Carrington St, Glenridding, after his body was found on the side of the road.
Police inquiries revealed he had been struck and killed by a car, with police saying at the time that the driver then fled the scene "without rendering assistance".
Now detectives are asking an anonymous caller to come forward after they claimed the vehicle involved returned to the scene and the occupants got out and checked on Pullen, who was still alive at the time.
A A$350,000 ($376,500) reward, offered by the New South Wales Government in 2019 for any information which leads to the arrest and conviction of those responsible, is still available.
Pullen was a father of three who died just days before he was to celebrate his 24th wedding anniversary. Speaking soon after his tragic death, Pullen's wife, Vicki, described the hit and run driver as "a coward".
"He was there to keep Singleton safe in case a bush fire broke out and just to save people's lives," she told 7 News at the time. At a media conference in 2019, where the reward was announced, his mother Gill Pullen said the past year had been "hell".
"We can't get closure. We can't go on with a life," she said.
"All I've got now is our memories from my son growing up.
"I carry his ashes around my neck. This has been on there since the day he was cremated. It's never been taken off."