The police officer who investigated the disappearance of Perth businessman Wayne Drewett nearly 10 years ago believes he was killed for more than $800,000 in cash raised to buy Eastern European diamonds that, unbeknownst to the beloved family man, probably never existed.

Speaking at the inquest into what happened to Mr Drewett, who disappeared in April 2003, senior sergeant Glen Potter said police believed Romanian-born Nick Stuart alias Niculae Stoian, was the likely "facilitator" of an elaborate diamond scam the Perth grandfather had fallen into.

Police believe Mr Drewett had obtained more than $800,000 in cash for the diamond deal, which they suspect had been moved from Mr Drewett's safety deposit box at Bankwest on St Georges Terrace into an identical box next to owned by Mr Stuart.

The only evidence Police have regarding the cash was the proximity of the two boxes, suspicious dates that had been accessed and testimony from a Bankwest employee who said she saw the front of Mr Drewett's box was stuffed with hundred dollar notes on April 11, 2003.

There was also the testimony of Mr Drewett's potential investors who said he was raising the money on behalf of a facilitator who he promised could resell the diamonds onto buyers at a great profit.

Although the employee saw the cash in April, when police searched Mr Drewett's box in May they found nothing.

The last time Mr Drewett's wife Joyce saw her husband was on April 14 at the Observation City Hotel, where they had rented a room.

He had told her he intended to buy a mustang and the pair had fought, the court heard.  He left saying he had more work to do on the diamond deal.

At 12.43pm the same day he withdrew $10,000 and opened a second safety deposit box, which police believe was the intended location for the proceeds of the diamond sale.

But he vanished before it could be used. 

"Wayne Drewett actually believed there was a diamond deal afoot," Snr Sgt Potter told the inquest.

"It’s the investigation's view that there probably wasn’t any diamonds."

When Mrs Drewett returned to the home she shared with her husband she discovered the backdoor was unlocked and uncharacteristically for her husband appliances had been left around the house.

But she did not report him missing for another couple of weeks because a group of his investors pressured her not to insisting everything was fine, Snr Sgt Potter told the court.

Snt Sgt Potter said police would likely have been in a much better position to find Mr Drewett if they had not been three weeks behind his disappearance.

"The possibilities would have been endless," he said.  "We would have had Nick Stuart in the country, we would have known about the diamond deal."

Mr Drewett was last heard from on April 15. By April 23 Mr Stuart had sold his car and equipment from a brick paving business he owned and flown back to Romania, a country that does not share extradition agreements with Australia.

Police had eventually discovered two burn phones registered by Mr Drewett under fake names, which were only used to call each other in the weeks before his disappearance, with one crucial exception that would lead them to Mr Stuart.

A phone registered under Mr Stuart's name had called one of the phones, police believe by accident.  When police looked into Mr Stuart they found he had spent three years in a WA prison for violence, dishonesty and guns offences.

They later discovered Mr Stuart was also at the time wanted for questioning by Romanian authorities over the disappearance of another man linked to another diamond deal who had procured $300,000 from investors for the deal in which he was "the facilitator" in 1996.

Between May and June several police searches of Mr Stuart's Marangaroo home involving ground penetrating radar revealed a hidden underground bunker made up of two rooms, one containing an arsenal of guns and ammunition, Snr Sgt Potter told the court.

Terrance Gardiner, who used to work as a book keeper for Mr Stuart after the pair met in prison also told the inquest of the secret bunker describing one of the two rooms as containing only a single bed.

Several books were also found in Mr Stuart's home including detailed guides for carrying out crimes, which notably included a book entitled 'Be Your Own Undertaker: How to dispose of a dead body'.

Devices for testing diamonds were also located.

"It confirmed to us that there was a likelihood that Mr Drewett had been killed," Snr Sgt Potter told the court.

"This led us to believe that Mr Stuart had the knowledge and the capability to do it."

He said although the Australian Federal Police and Romanian authorities had worked together to locate Mr Stuart in Bucharest – they had not been successful in returning him to Australia.

Counsel assisting the coroner Kate Ellson in her closing submission yesterday advised the coroner that beyond a doubt Mr Drewett was dead.

"There is a very real possibility that Mr Drewett was killed for the money he raised for a diamond deal," she said.

Since April 15 Mr Drewett has never accessed any of his known bank accounts, email accounts, phones, or attempted to reclaim his car which was believed to have been dumped outside Perth airport, she said.

There were also no Medicare records of him purchasing medication he needed for a serious heart condition.

Speaking outside court Mr Drewett's daughter Debra said the family were relieved the inquest had moved ahead more than 9 years after he went missing, but were still looking for answers.

"I don't think that will every go away until we have remains that we can put to rest," she said.

"If anybody still has any information that might reveal where my husband's remains are that might give my family closure."

Ms Drewett described her father was a "wonderful family man," who was "loved dearly".

"I feel like I'm back to day one again – it's been very hard for everyone," she said

The coroner is expected to hand down his findings into Mr Drewett's possible death in December.

Ms Drewett said the family wanted him finally declared dead.