A prospector who stumbled across the abandoned campsite of a couple who went missing in remote Western Australia said it looked like it had been vacated for days and a wasp nest had even formed inside one of their vehicles.

Key points: Raymond and Jennie Kehlet were reported missing on March 19, 2015

Raymond and Jennie Kehlet were reported missing on March 19, 2015 They had been prospecting in a remote spot with their friend, Graham Milne

They had been prospecting in a remote spot with their friend, Graham Milne Mr Kehlet's body was found down a mineshaft, but his wife vanished

Robert Blair was giving evidence at an inquest into the case of Raymond and Jennie Kehlet, who went missing on a prospecting trip near Sandstone, about 700 kilometres north-east of Perth, on March 19, 2015.

They were reported missing about 10 days later after their dog, a great dane named Ella, wandered into a caravan park in the townsite.

An extensive air and land search began, and the body of Mr Kehlet was found about three weeks later down an abandoned mineshaft.

No trace of Ms Kehlet has ever been found.

The Kehlet's pet dog Ella raised the alarm after wandering into Sandstone, 30km away from their campsite. ( Supplied: WA Police )

The couple were joined on the trip by a friend, Graham Milne, who left the area three days after arriving and who the inquest heard remains a suspect in the case.

Mr Blair testified that he and his prospecting companions first came across the Kehlets' campsite on March 27 when they were looking for a new place to set up camp for themselves.

He said when they drove past the site they did not see any people, but saw a dog sitting on its haunches.

Mr Blair said he also saw, further up the track, a quad bike that appeared to be partially hidden.

Witness thought smell was dead kangaroo

He told the inquest the next day he and his companions used a different track to go back to the site where they had chosen to set up their camp.

He said over the next few days they noticed a smell in the area, which they thought was a decaying kangaroo, but it was not unusual and went away after heavy rainfall.

On March 31, Mr Blair said his camp received visits from council workers who informed them two prospectors were missing in the area.

Later that day, he and one of his friends went for a walk in the bush to look for prospecting sites and they again came across the quad bike, which they realised had not been moved since they last saw it.

"I was a bit concerned that no one had seen the quad bike. It was obvious to us it had been there for a while and that the camp had been abandoned for a little while," he said.

Raymond Kehlet's remains were found during a search for the couple, down a mineshaft. ( Supplied: WA Police )

He said they then walked towards the site.

"We called out, no one answered, the dog wasn't there and we walked into the camp," Mr Blair said.

"It was quite obvious … the camp had been vacated for a while. We thought they might have been missing for a bit longer than people thought."

Wasp nest spotted inside car

Mr Blair said he found a note on one of the vehicles that had been left by council workers who had visited the camp earlier.

He said he wanted to let them know about what they had seen, so he opened one of the unlocked doors of a vehicle to try to find a pen to write down the council worker's phone number.

"On the back right hand rear door there was a big wasps nest … about 20 to 30 centimetres in diameter," he said.

"It was quite large on the inner door handle attached to the leather.

Raymond Kehlet's remains were found down a mine shaft, but Ms Kehlet has never been found. ( Supplied )

"I thought people had not been there for a while because it takes a few days to build a nest."

Mr Blair said he also saw a wallet in the car along with other documents, but he did not open or inspect them.

He testified there were food containers in the campsite, some of them open, and there were also clothes still on the line.

A loaded rifle, out of its case, was found on the front seat of one of the vehicles, but Mr Blair said he did not see the weapon because the council workers had removed it.

He and his friend then decided to look in some of the mineshafts around the area in case someone may have fallen down, but they did not see anything and returned to their campsite to notify authorities about what they had found.

'That's him': Witness says she saw 'agitated' Milne

Another witness later told the inquest she and her husband saw an "agitated" motorist pulled over by the side of an unsealed road in the Sandstone area, early in the morning, on the day Mr Milne said he left the campsite to return to Perth.

Georgina Granville said she and her husband were driving on Paynes Find-Sandstone Road when it was still dark on March 22, when they saw the man, who she described as either being bald or having a number one crew cut.

Ms Granville said they slowed down their car to see if he needed help but the man waved them on.

She described him as being "quite agitated" and "quite aggressive … as if to say to 'go away, shoo'."

Graham Milne accompanied Raymond and Jennie Kehlet on their fateful prospecting trip. ( ABC News: Joanna Menagh )

Ms Granville told the inquest later when they were back in Perth she saw something on television about the Kehlets' disappearance, that showed footage of "their friend".

She testified she turned to her husband and said "that's the guy I saw … the man we saw on the side of the road, that's him".

The inquest has heard Mr Milne has maintained to police that he did not use the unsealed Paynes Find-Sandstone Road to leave the area, and instead travelled on the sealed Mount Magnet-Sandstone Road.

However, police have testified a GPS coordinate taken from Mr Milne's car put it on the unsealed road on that day.

The inquest has also been told Mr Milne's car was not captured by CCTV cameras at a service station that records all cars travelling on the Mount Magnet-Sandstone Road.

Mr Milne denies having anything to do with Mr Kehlet's death and the disappearance of Ms Kehlet.

He is scheduled to give evidence later in the inquest.