A suspect in the deaths of his two "good friends" while prospecting in remote Western Australia has been forced to testify at their inquest despite concerns he could incriminate himself.
Raymond Kehlet, 47, and his wife Jennie, 49, never returned home alive from a prospecting trip to Sandstone, about 660km north of Perth, in March 2015 with their colleague Graham Milne.
Mr Kehlet's body was found about one month later down a mineshaft, some 1.8km from their camp site, but Ms Kehlet's body has never been found.
Last week, the WA Coroner's Court heard from Detective Sergeant Stephen Cleal, who said every person of interest in the case had been eliminated, except for Mr Milne.
But police have never charged Mr Milne despite conducting two interviews, including one that lasted more than 12 hours, and receiving four statements from him.
Mr Milne's lawyer Glenn Cridland told the inquest on Wednesday that his client wanted to "exercise his right not to answer questions" because "they may have the tendency to incriminate him".
"One can see where the police case is going," he said.
Lawyer representing police Sarah Keighery told the court there was still no intention to charge Mr Milne.
Coroner Ros Fogliani offered Mr Milne a section 47 certificate, which means his evidence at the inquest cannot be used in any future criminal proceedings against him if she accepts his testimony is truthful.
Mr Milne testified he first met the couple in 2010 when they were all working at Fortescue Metals Group's Cloudbreak mine in WA's Pilbara region.
He described the couple as like "two peas in a pod" and said he never saw disharmony between them.
They were interested in prospecting and Mr Milne visited their Beverley farm to train them.
Mr Milne testified they had planned to abseil during a trip to Mt Palmer but the couple cancelled due to a family illness, so he went alone.
But Mr Milne said the couple was not planning to abseil down mine shafts during their trip to Sandstone.
"I wouldn't allow anyone else to go down a mine shaft without proper gear," he said.
Mr Milne said they kept their plans quiet.
"Ray wanted to keep it, as he called it, secret squirrel ... he didn't want anyone to know," he said.
The inquest continues.