Forensic officer Mark Gellatly grilled over ‘vacuum theory’ related to Greg Lynn’s shotgun

A specialist in bloodstain pattern analysis has been accused of lying during a tense cross-examination in the missing campers trial.

Greg Lynn's Barathrum Arms SP-12 shotgun was allegedly used to murder Carol Clay. Picture: Supplied/ Supreme Court of Victoria

Accused High Country killer Greg Lynn’s legal team have accused a forensic expert of lying and collaborating with prosecutors to give misleading evidence.

The former Jetstar captain, 57, is standing trial for the murders of Russell Hill, 74, and Carol Clay, 73, who vanished during a camping trip to the Wonnangatta Valley in March 2020.

During tense questioning in the Supreme Court on Thursday, defence barrister Dermot Dann KC interrogated forensic officer Mark Gellatly — a specialist in bloodstain pattern analysis — about a “vacuum theory” related to his client’s shotgun.

Mr Gellatly examined Mr Lynn’s Barathrum 12-gauge shotgun, earlier telling the jury no blood was found inside the barrel but a partial DNA profile was obtained.

Russell Hill, 74, and Carol Clay, 73 were allegedly murdered by Greg Lynn.

As part of his testing, Mr Gellatly said he had given consideration to a “vacuum theory”.

“The theory is when the projectile exits, it creates a vacuum and … if it’s close enough to blood that’s in flight, that blood can be carried back into that barrel,” he told the court.

Mr Gellatly said he was provided information by the case’s lead detective that the firearm had shot Mrs Clay from about three to four metres away — too far for the vacuum to work.

There were several heated exchanges during an hour-long cross-examination, as Mr Dann grilled Mr Gellatly about why he had failed to mention the theory in his reports or his hundreds of pages of notes.

There has been a lot of discussion about whether blood was carried back into the barrel of Greg Lynn’s 12-gauge shotgun.

He went on to accuse the forensic expert of discussing the theory with prosecutors before he began his evidence on Thursday afternoon but would not admit it because it harmed their case.

“I can’t actually recall if we spoke about that or not,” Mr Gellatly said.

The defence barrister took Mr Gellatly to transcripts from a preliminary hearing, in which he denied discussing the theory with the prosecution.

“So that’s just false evidence, that’s just a lie?” he said.

“It wasn’t a lie,” he said.

“Do you have some ongoing difficulty with your memory?” Mr Dann asked.

“No I don’t,” he replied.

Mr Dann accused Mr Gellatly of a “flagrant breach” of the rules of evidence and procedure relating to expert evidence, and that he was not qualified to give an opinion on the theory nor was it relevant to the case.

Mr Gellatly conceded he was not a ballistics expert and theory was outside his field of expertise, but claimed it could have helped determine the proximity of the gun.

While no blood was found on Mr Lynn’s shotgun, the jury was earlier told a partial DNA profile was obtained from the barrel but it could not be matched with a person.

“Based on the limited information, no comparisons were done,” Mr Gellatly said.

The forensic officer also examined the canopy of Russell Hill’s Toyota LandCruiser in February 2022, which revealed six suspected blood stains and an “apparent fatty deposit” inside the passenger side compartment of the canopy.

The rear canopy of Mr Hill's LandCruiser. Picture: Supplied

The forensic officer also examined the canopy. Picture: Supplied

There were six suspected blood stains and an ‘apparent fatty deposit’ inside the passenger side compartment of the canopy. Picture: Supplied

Testing of the stains could not confirm it was blood, Mr Gellatly said, but he noted the canopy had been damaged by heat which could distort results.

“I made the assumption it was blood but we couldn’t confirm it,” he said.

Mr Gellatly said DNA testing of the fatty deposit and one of the blood stains lent “extremely strong support” that it originated from Mrs Clay.

Analysis of the stains also indicated a “forceful event” had taken place but there were not enough stains to make a finding on what it was, noting a cough or sneeze were possible explanations.

According to Mr Lynn’s account, Mrs Clay was accidentally shot in the head as the two men struggled over a shotgun.

The ex-pilot claimed she was crouched next to Mr Hill’s LandCruiser when the shot passed through the side passenger mirror and struck her in the head.

On Thursday afternoon, Justice Michael Croucher told the jury the trial would not return until Monday as the next witness, Detective Sergeant Brett Florence, was “crook” and unable to attend court.

But he said the trial was ahead of schedule, as he reminded them not to discuss the case or conduct their own research over the weekend.

The trial continues.