The judge in the trial of five people accused of a million-dollar gold theft in Western Australia's Goldfields has told the jury to "closely scrutinise" the evidence of a key prosecution witness and that the defendants are "entitled to the benefit of any doubt". 

Judge Christopher Stevenson today is giving legal directions to the 14-member jury in the Kalgoorlie District Court trial before a ballot is held to determine the final 12 who will vote on a verdict.

In total, there are 10 counts on the indictment which means the jury will have to consider a separate verdict for each charge.

More than 50 exhibits have been tendered during the trial, which is in its fourth week after hearing evidence from eight witnesses. 

The charges relate to the alleged theft of 8,465 tonnes of gold-bearing ore from the Greenfields Mill near Coolgardie between December 2018 and January 2019.

The gold the ore produced, and which was sold to the Perth Mint, was worth $1.17 million based on metal prices at the time.

The case hinges on a decade-old conversation between Peter Bartlett, the founder of FMR Investments which owns Greenfields Mill, and the company's former general manager, Patrick Rhyan Keogh. 

Mr Keogh, 42, has testified that Mr Bartlett gave him permission to profit off a waste stockpile sometime in late 2012 or early 2013, and that he "didn't have to ask him twice", before it was treated at Greenfields Mill five years later.

"I didn't give him permission," Mr Bartlett told the court on at least two occasions during his testimony, as defence lawyers have continually tried to undermine his credibility as a key prosecution witness. 

Mr Keogh and former Greenfields Mill manager Christopher Robert Burns, 76, have both pleaded not guilty to stealing as a servant and other charges relating to the proceeds of an offence.

Mr Keogh has admitted that $590,411 was sent to his private business account on March 13, 2019 from Aqua Alluvial Pty Ltd.

The private company is controlled by two of the co-accused, Simon Leslie Gash, 57, and his business partner, Russell Wilson Holden, 51, who are fighting money laundering and fraud charges.

The prosecution alleges the Kalgoorlie prospectors knew about plans to combine ore they mined with ore owned by FMR Investments.

Former mill superintendent Morgan Whitney Dombroski, 33, has also pleaded not guilty to charges alleging she received $90,000 cash from Mr Burns.

Judge Stevenson said the "critical question of fact in this trial" was the alleged conversation between Mr Keogh and Mr Bartlett, and that the jury should rely on "common sense and collective life experiences" to determine a verdict.

He said the jury must "carefully scrutinise" the evidence of Mr Bartlett to determine his "credibility" as a witness, adding that they must be satisfied beyond reasonable doubt of his "truthfulness, accuracy and reliability" before convicting Mr Keogh.

Five trials in one

Judge Stevenson told the jury to "ruthlessly put aside the evidence" that was not admissible against a particular accused, saying the case was effectively "five separate trials" and not all the evidence was relevant to each defendant.

"You must look at each count separately and consider only the evidence relevant to that count," he said.

Judge Stevenson told the jury they could not read anything into the fact that four of the accused did not testify during the trial.

"That proves nothing, one way or the other, and your duty is to consider the evidence in the trial against the accused, and answer if the state has proved its case beyond reasonable doubt."

The same applied in respect to Mr Keogh, who did not participate in a police interview but took the witness stand during the trial, the judge said.

"If you have difficulty accepting his evidence, but think it could be possible [the conversation with Mr Bartlett occurred], then it would be your duty to return a not guilty verdict as there would be reasonable doubt," he said.

Lawyers criticise investigation

Earlier, the court heard criticism of the police investigation by defence lawyers.

Mr Burns's lawyer, Tom Percy KC, told the court the prosecution case was "misconceived" and based on a "very poor investigation" that "raised more questions than it answered".

He said the investigation, run by the Kalgoorlie-based Gold Stealing Detection Unit, relied on "guesswork and speculation" and he argued there was no evidence to prove his client did anything "untoward".

Mr Keogh's lawyer, Seamus Rafferty, said the investigation was "flawed" due to the level of involvement by a private lawyer and other directors of FMR Investments in crafting a police statement for Mr Bartlett.

Mr Rafferty pointed to testimony from Detective Sergeant Chris King, who told the court he "pre-drafted" the initial statement for Mr Bartlett based on the "known facts of the case at the time".

The court heard there was significant discussion with an external lawyer, Kirsten Scott, over several months before Mr Bartlett signed a formal statement on November 18, 2021.

The FMR Investments founder signed an amended statement on February 23, less than a fortnight before the trial began on March 7.

Mr Rafferty told the court the process was "contrary to what you would consider best practice".

"As we heard from Detective [Senior Constable Andrew] Kettle, an experienced copper who's good at his job, best practice is when you sit down with a witness and they give you a story, a running narrative," he said.

"This [statement] wasn't Peter Bartlett's story … this was what Detective [Sergeant] King said.

"It's not the right way to conduct an investigation, simply to present someone a fait accompli and say: 'Is that right?'

Mr Rafferty said he was "not suggesting anything nefarious or surreptitious" had occurred on behalf of police, but he maintained "best practice" was not followed.

"There was an obvious potential for conflict," Mr Rafferty told the court.

"FMR's lawyers should never have been involved in drafting statements ... it's certainly not best practice as far as an investigation is concerned."