The lead forensic investigator of the 2018 Reedy Swamp/Tathra bushfire has revealed he only received crucial pieces of evidence just weeks before the coronial inquiry was due to begin.
Detective Senior Sergeant Craig Harris, who has investigated up to 30 bushfires, told the inquiry on Tuesday the conclusion of his investigation contradicted later photographic and eye-witness evidence around the location of the origin of the fire.
Later evidence showed the fire likely began at a different power pole to the one both he and NSW Rural Fire Service operational officer Inspector Angus Barnes concluded to be the point of origin of the fire.
"I've thought long and hard about this. I was a little annoyed, because did I miss something?" Detective Senior Sergeant Harris told the inquiry.
The senior fire forensic investigator told the inquiry he believes a tree likely struck insulators on a powerpole, but admitted other theories are "plausible".
He said it took six to 12 months to receive statements and reports from witnesses, which allowed him to "exclude" certain theories.
The inquiry, which began this week under the guidance of Deputy State Coroner Elaine Truscott, earlier heard dead trees, infested with termites, likely fell on powerlines, igniting the fire which burned through more than 1000 hectares of forest, causing $63.5million worth of damage, and destroying 56 homes and 35 outbuildings.
Detective Senior Sergeant Harris said the statement provided by volunteer firefighter Andrew Parsons, who was tasked with property protection at 580 Reedy Swamp Rd in "gusty and swirling" wind conditions, was only received by his office three weeks ago.
The fire began just a few kilometres from Bega, with hot temperatures and strong winds pushing it towards Tathra.
Investigators initially studied the impact of the fire from the air to locate the area most likely to be the point of origin, with Detective Senior Sergeant Harris admitting investigators disagreed a number of times.
He said "in hindsight" tracking the fire ground differently could have lead to their conclusion matching the later witness evidence.
Detective Senior Sergeant Harris said he disagrees with the conclusion reached by electrical engineer Trevor Blackburn, while also admitting he is not an expert in electrical infrastructure.
He said the tree in question could have fallen either side of a power pole, landing on live powerlines, and when asked by counsel assisting Adam Casselden SC which of his two theories were more likely, said he could not "weigh one over the other".
He said in his experience trees do not fall quickly due to fire damage, pointing at other factors for the tree fall.
There were varying areas of fire intensity around the easement where the tree fell, near 580 Reedy Swamp Rd, with the fire becoming "intense" about one kilometre to the east of its origin, he said.
When questioned, Detective Senior Sergeant Harris said while all infrastructure evidence was collected and secured, the fact the trees were not has removed the opportunity for further expert investigations.
The inquiry also discussed a second fire, which started "hours later" in the same area, joining up with the first, likely started by spotting from the first, he said.
Inspector Barnes also gave evidence on Tuesday, saying he pinpointed the point of origin to within an area around three metres in diameter.
An inquiry will only held if the coroner decides that more evidence is needed to determine the cause and origin of a bushfire.