Rumours have circulated for decades about a mysterious panther-like cat roaming bushland fringes in NSW. Last Saturday, a startled couple from Goulburn became the latest witnesses to shoot a grainy, quick-fire frame of the large feline predator - which they insist was "a panther".

Jeff and Ruth Gulson were eating lunch on their 20-acre property at Goulburn when through the kitchen window, the animal came into view.

Moving onto their balcony, which overlooks a valley and bushland, they remained mesmerised by the creature for the next 15 minutes.

"Let's be clear, this was certainly no dog," Mr Gulson said. "It was cat-like in its movement but it was a bigger than a sheep.

"We had the binoculars out. We watched it move. We know what we saw ... and what we saw ... 110 per cent was a panther."

For decades, huge black cats have been sighted by rural residents across three large national parks that connect across the mountains west and north of Sydney - the Kanangra-Boyd, Blue Mountains and Wollemi parks.

However, a similar creature has also been observed for decades around Goulburn and the Kangaroo Valley.

At various times over the past 20 years, the NSW government has treated the story as more than just a myth.

In a 1999 letter to then National Parks and Wildlife Service director-general Brian Gilligan, Department of Agriculture head Kevin Sheridan warned: "The reports are becoming too frequent for us to ignore the possibility. To ... do so could bring into question government's duty of care."

That letter only came to light after a member of the public submitted a freedom of information request for all state government-held documents relating to big cat sightings.

Those same files also revealed how the government had commissioned a wildlife ecologist, Johannes Bauer, to provide his "expert opinion".

He concluded: "Difficult as it seems to accept, the most likely explanation of the evidence is the presence of a large, feline predator. In this area, [it is] most likely a leopard, less likely a jaguar."

In 2008, then premier Nathan Rees admitted he too was a believer. "It is easy for all of us to dismiss these things ... but if we're actually wrong then there is an altogether different set of scenarios."

More recently, however, the O'Farrell government declared the big cat file officially "closed" after it commissioned a New Zealand invasive species expert, John Parkes, to look into it. He described the 500 eyewitness accounts as "at best prima facie evidence", saying "large dogs, large feral cats or swamp wallabies" were the likely candidates.

Until a conclusive photo or video footage emerges, witnesses and believers will continue to face ridicule. 

A week on from his own encounter, Mr Gulson now realises that he was given the "perfect opportunity" to silence the sceptics. 

"Our photo was taken from about 300 metres away and we zoomed in as close as we could get. 

"But I'm kicking myself now that we didn't think to take the pictures earlier as at one stage, we could have shot the animal from about 100 metres away. Had we sneaked up a bit closer, there was every chance we could even have got as close as 50 metres."

Mr Gulson has since been inundated with feedback from people across the local community who have seen the animal.

"It's floating around, and based on what people have said, I believe there is more than one.

"I hope it crosses my path again. The camera is ready."

Do you know more? Email editor.scregister@fairfaxmedia.com.au

goulburnpost.com.au