Mr Pullen was found dead by the side of Carrington Street at Glenridding about 5.30am on September 29, 2018.

The 43-year-old had a day earlier arrived in the Hunter Valley to assist the NSW Rural Fire Service prepare for the upcoming bushfire season.

Initially treated as a hit-and-run, the mystery prompted a two-year investigation involving multiple appeals for information and a $350,000 reward.

In October last year, after receiving an anonymous tip-off, Strike Force Awabakil detectives arrested and charged Joshua Knight, 29, and Nicole Mason, 30, with Mr Pullen's murder.

Police allege that Mr Knight had been driving a white Toyota HiLux utility that struck Mr Pullen in the early hours of the morning before leaving the scene.

Detectives claimed the vehicle returned a short time later and Ms Mason got out and "finished the job", striking Mr Pullen in the head with an object. Mr Knight was also charged with dangerous driving occasioning death and failing to stop and assist after an impact causing death.

But as the matter dragged through the courts, Mr Pullen's cause of death became an issue for the DPP with an autopsy revealing Mr Pullen would have died from the initial impact of the car.

The Newcastle Herald understands that when the DPP finalise the charges against the pair in Newcastle Local Court on Wednesday that both Mr Knight and Ms Mason will have their murder charges withdrawn.

Ms Mason will instead be charged with attempted murder, with the DPP alleging she had the intent to kill Mr Pullen despite the injuries that would have already claimed his life.

Mr Knight is expected to remain charged with failing to stop and assist after the fatal crash.

Both are behind bars and, due to the DPP's determination, are expected to make applications to be released on bail in the near future.

Two other women - Lilli-Jane Kaye Sales and Ivy-Jean Ward - accused of being an accessory after the fact to Mr Pullen's murder are also expected to have their charges reduced.

Former Newcastle Nomads boss Bradley Bowtell has also been linked to the cover-up of Mr Pullen's death. He has pleaded not guilty to two counts of concealing a serious indictable offence and hindering an investigation and will face a hearing in Muswellbrook Local Court in September.

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