The coronial inquiry into 2013's bushfires heard another five days of evidence last week, including from three experts who testified at the same time, a relatively recent development in the court system known as a "hot tub".
The three men in the tub in Katoomba were Inspector Graeme Moore, from the Fire and Rescue NSW fire investigation unit, station officer Michael Forbes, also from Fire and Rescue, and Superintendent Bob Mathieson, manager of fire investigations for the Rural Fire Service.
All three played a role in investigating the Linksview Road fire of October 17, 2013, which destroyed 194 homes in Winmalee and Yellow Rock.
The idea behind them giving evidence together is so they can discuss the same issue at the same time, so reducing the chances of misunderstandings.
It also helps keep testimony shorter and to the point, rather than having to ask the same questions on three separate occasions to each of the witnesses, according to the NSW Department of Justice.
The men were asked whether spotting from the State Mine Fire could have caused the Springwood fire. While spotting has been known to occur several kilometres from a fire front, they agreed the 43-kilometre distance was just too great to consider spotting as the source of the fire.
The men admitted there had been some debate about who should investigate the October 17 fires.
Superintendent Mathieson said: "There was a discussion about whose jurisdiction it was. The actual fire occurred in an RFS area ... therefore the investigation was the RFS even though power lines and the tree were in Fire and Rescue jurisdiction.
"There has been some rivalry over the years [between the organisations] ... but the situation has improved since then."
Mr Forbes told the inquiry he flew over the scene of the Springwood fire the morning after it happened when he could see clearly how the fire had spread from its point of origin - a tree coming into contact with power lines outside 108 Linksview Road.
"It was apparent from the burning that the fire had spread from this location."
Later, an experienced arborist who examined the tree whose branch had fallen on to power lines in Mt York Road, igniting the Mt Victoria fire, said it had obvious defects that should have raised alarm bells.
Adam Tom, a consultant from Queensland, said he examined the tree at Mt York last week and also checked the broken branch which is being stored at Katoomba police station.
The tree showed structural defects - it was badly asymmetrical and leaning at an angle of almost 40 degrees. It also had scars, or wounds, where branches had previously dropped off. The broken-off branch had been attacked by fungi and termites and was more than 50 per cent hollow.
The presence of such a tree near power lines should have warranted "a closer look", he said.
"It would further appear that tree inspections may not have been correctly performed and, as such, failure has occurred."
The inquiry, being held before coroner Fiona Toose at Katoomba, will sit again for a final week from December 7.