Prosecutors in the trial of former Jetstar pilot Greg Lynn have urged jurors to reject the 57-year-old's account that the deaths of two elderly campers were accidental as an "elaborate fiction".

During closing arguments of the weeks-long double murder trial, prosecutor Daniel Porceddu argued Mr Lynn's decision to cover up the deaths of Russell Hill and Carol Clay was a "deliberate, calculated and protracted" series of incriminating actions.

"The most extreme of these actions is the burning of the bodies of Mr Hill and Mrs Clay eight months after they were murdered," he said.

"This step, along with several others taken by the accused, were designed to obliterate any possibility that there would be any forensic evidence which would reveal anything about the manner in which they died.

"The only reasonable explanation for the cover-up was he knew he had murdered them and, if the scene was left as it was, the forensic evidence would reveal that fact."

But in response, defence lawyers tore into the prosecution case, saying it had deteriorated from the "problematic category that it started in" into a "hopeless mess".

"That regression was marked by a series of lowlights in the presentation of that prosecution case," Dermot Dann KC said.

The barrister went on to outline 17 purported "lowlights", some of which were described as desperate and half-baked theories, others allegedly a selective approach to evidence that didn't suit the prosecution's account.

One example given was the prosecution purportedly getting statements about Mr Hill's "long history of association with shotguns" from his family, but not asking about that when those family members were on the witness stand.

Prosecuting lawyers slam Mr Lynn's account as 'completely implausible'

The former Jetstar pilot stands accused of murdering retirees Russell Hill and Carol Clay at a remote campsite he shared with the pair in Victoria's high country in March 2020.

Central to the case is a night-time dispute that unfolded between the two men, which Mr Lynn's lawyers argue resulted in separate fatal, accidental struggles involving Mr Lynn's gun and a knife.

In a closing address that ran about three hours, Mr Porceddu argued there were a number of reasons this account was "completely implausible", including Mr Hill loading the gun and knowing how to fire several warning shots, despite purportedly confiscating it from Mr Lynn's vehicle out of concern about the risks of deer-hunting.

The prosecutor also pointed to several instances in Mr Lynn's November 2021 police interview in which he referred to the weapon as a rifle, when it was a 12-gauge shotgun.

But Mr Porceddu argued the existence of a rope running between the elderly couple's vehicle and a portable camping toilet was "the house of cards" around which the accused's account of the struggle fell apart.

The barrister said if Mr Lynn tried to grab the shotgun and disarm Mr Hill in the manner he described in his police interview, he "would've become hopelessly entangled in the rope".

"We urge you to see the accused's account for what it is: a carefully constructed fiction developed over one year, eight months," he told the court.

"During that time, the accused was able to gather through the media an understanding of the evidence that was emerging."

No motive or method, but charge proven: prosecution

Campers, hunters and workers in the Wonnangatta Valley have been called into the witness box as the trial has unfolded over about four weeks.

Mr Porceddu's address went to evidence some of those people gave about Mr Hill's character to argue against the theory that Mr Hill flew into a "homicidal rage" during the dispute with Mr Lynn.

"Despite the best efforts of the defence asking questions about Mr Hill's use of [a] chainsaw, of his long-term antidepressants and his penchant for Cougars [bourbon and cola] and rum, there's really no evidence of Mr Hill behaving in an aggressive manner towards other people," he said.

From the outset of the trial, prosecutors said they did not know the motive for or the circumstances of the retirees' deaths, other than that Mrs Clay was shot in the head.

However, they insisted the circumstances of the two violent deaths in close proximity pointed to the pair being killed without lawful justification.

Mr Porceddu told the court it was likely Mr Lynn "bore some animosity" towards the pair because of Mr Hill's drone, arguing the 74-year-old was killed first before Mrs Clay was "eliminated because she was a witness".

By contrast, defence teams said the prosecution had not come "remotely close" to disproving Mr Lynn's account of the accidental deaths beyond reasonable doubt.

Mr Dann said his team knew at the outset of the trial that Mr Lynn had provided more than 1000 pieces of information to police during his interview.

"We were confident at that stage that scrutiny — which we were inviting, embracing — would demonstrate that of those 1,057 pieces of information, the prosecution would not be able to demonstrate one of them was a lie," he said.

"We're still in that position."

Before Tuesday's hearing got underway, Justice Michael Croucher told jurors the closing arguments could run for more than a day before he would instruct them on the issues in the case.

"Once that occurs, then you'll go out to consider your verdicts," he said.