Rural Fire Service and police chiefs on Friday released investigations into the blazes that destroyed property and threatened homes in Sydney's west and the Blue Mountains on Tuesday.
A home was lost at Marsden Park as a result of a fire police believe was deliberately lit, one of around 63 blazes that hit NSW at the height of the emergency.
Another bushfire, at Winmalee, which has burnt through more than 1000 hectares of bushland, came after a back-burning operation jumped containment lines.
Police Assistant Commissioner Alan Clarke said a probe into the Marsden Park fire indicated it was deliberately lit.
"There are crime scene indicators that lead us to suspect arson activity," Mr Clarke said.
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"It's certainly under significant investigation by strikeforce Toronto and local area command detectives."
And hazard reduction operations were responsible for the fire at Winmalee after a change in weather conditions.
RFS Deputy Commissioner, Rob Rogers, says National Parks staff were leading back-burning at Winmalee when unforeseen winds caused
the blaze to escalate on Tuesday.
"They were around 90km/h, and that tested control lines on that hazard reduction and it did escape," Dep Comm Rogers said.
That blaze has now been contained, but is still burning.
He says power lines falling onto trees were responsible for the bushfire near Windsor Rd, while investigators hadn't determined what caused the fourth big fire at Castlereagh.
The RFS also said it was examining whether a fire on Thursday at Wyee, on the Central Coast, was caused by back-burning.
That fire caused traffic chaos when it forced the closure of the M1 motorway.
"There's a review going on today into the Wyee fire, as in, did it come from a hazard reduction," Dep Comm Rogers said.
Meanwhile, residents near national parkland at Potato Point, on the NSW south coast, say authorities are ignoring their pleas to boost fire protection in the area.
They want the state government to restore a firebreak between Eurobodalla National Park and the community that was removed in 1995.
