Two campers allegedly murdered by Gregory Lynn in a remote national park were “childhood sweethearts” who had kept their relationship secret for 15 years, police will allege.

Carol Clay, 73, and Russell Hill, 74, had travelled to Wonnangatta Valley on March 19, 2020, for a short camping trip in the remote wilderness when they vanished sometime after 6pm the following day.

Police allege Lynn, a former Jetstar pilot, killed the pair following an altercation in the national park and dumped their bodies.

The 56-year-old has pleaded not guilty and will contest the charges.

In a summary of the case against Lynn provided to the Melbourne Magistrates’ Court on Tuesday, police allege Hill and Miss Clay had rekindled a relationship about 15 years earlier and would go on regular camping trips to “spend time together”.

The pair were childhood sweethearts who had drifted apart and had children with other partners, documents tendered to the court said.

Hill had been married to another woman for 51 years at the time of his death, and police facts tendered to the court revealed Hill’s wife believed he had gone camping alone.

“Those close to them believe that they kept their relationship a secret to spare Hill’s family from distress,” the police statement of facts read.

On Tuesday, the court heard Clay may have been shot in the head as Hill and Lynn fought over a shotgun.

The 56-year-old Caroline Springs man has faced the Melbourne Magistrates’ Court this week for a committal hearing, where magistrate Brett Sonnet will decide whether there is sufficient evidence for Lynn to stand trial in the Supreme Court.

On Tuesday, forensic expert Mark Gellatly was called to give evidence about the forensic examination of evidence recovered during the investigation.

Under questioning by defence lawyer Dermot Dann KC, he was asked by investigators to consider a “scenario” in which Clay was accidentally hit when Hill grabbed Lynn’s shotgun.

“The two were wrestling over the gun, causing an accidental discharge,” Dann said.

“Ms Clay was shot in the head.”

Gellatly told the court he was asked to investigate this possibility but ultimately said he could not confirm or exclude the scenario based on the limited evidence available.

Former pilot Gregory Lynn. Photo / Supplied

He told the court that DNA and biological material linked to Clay were found on the canopy of Hill’s vehicle.

“It’s possible they were connected (to the scenario),” he said.

Crown prosecutor John Dickie complained about the scenario being raised by Dann, saying it “might not” reflect the case against Lynn.

Dann said it was “important” to understand the context in which forensic officers ran their investigation.

Earlier, the court was told that Lynn was secretly recorded by police just months after Hill and Clay vanished while camping in the Victorian Alps.

Detectives from the missing persons squad visited the former Jetstar pilot’s Caroline Springs home on July 14, 2020 – more than two years before he was charged over the alleged murder.

Giving evidence before Lynn’s committal hearing on Tuesday, Detective Senior Constable Abbey Justin said his blue Nissan Patrol had been photographed leaving the area a day after the campers were allegedly killed.

The Melbourne Magistrates’ Court heard police had tracked the phone movements of the missing pair to an area around Mount Hotham.

Detective Senior Constable Justin said the phone was identified as being in the area of an automatic number plate recognition system camera around 9.45am on March 21, 2020 – the morning after they were allegedly killed.

Twelve cars were recorded by the camera during the time period but only one wasn’t allegedly picked up by other cameras entering the Wonnangatta National Park – Lynn’s.

“The 11 cars were taken out of the equation because they activated cameras one and two,” she said.

“According to the information from Telstra, the deceased’s phone was in the area at that time,” she said.

In July, she quizzed Lynn in the kitchen of his home about his movements through the park and the colour of his vehicle.

“At that point he was a witness,” she said.

“We were there to find out the movements of his car and confirm who was driving.”

The court heard Lynn’s wife Melanie could be heard working from home in the background of the recording.

In the photograph taken by the automatic number plate recognition system, Lynn’s vehicle was a dark “bluish” colour but in the driveway of his home Detective Senior Constable Justin saw it was painted beige.

“I was under the belief that it was the same vehicle,” she said, telling the court she snapped a photo of the vehicle when leaving.

The interview was allegedly recorded by a “micro-recorder” and, under questioning from Dann, she admitted she hadn’t “cautioned” Lynn.

“I would never give a witness a caution,” she said.

Lynn, who has denied killing the pair, could be seen taking notes as he watched crown prosecutor John Dickie call witnesses to give evidence.

Police have yet to reveal why they believe the former Jetstar pilot killed the pair, laying out a circumstantial case against Lynn.

Eight witnesses have given evidence before the committal hearing, which has been adjourned until January 23 to hear from three more.

Over the course of Monday’s hearing, prosecutors sought to establish a timeline of the disappearance and alleged murder of the two campers.

Witnesses told the court they were seen arriving on the afternoon of March 19 after driving from Melbourne for a camping trip.

They had been long-time friends and Hill was known to be a well-prepared and enthusiastic camper, with the last confirmed contact received over high-frequency radio on March 20.

Remains, later confirmed to be the missing campers, were found buried in bushland near Dargo about 40km from the original campsite.

Lynn was charged with two counts of murder in November 2021 and has spent more than a year on remand.

The hearing before magistrate Brett Sonnet continues, but will not hear further evidence until Monday.