Margaret Anne Otto, of Risdon Vale, and Bradley Scott Purkiss, of Elderslie, are both charged with the murder of Mr Davies. 

Ms Otto and Mr Purkiss both pleaded not guilty and face trial together. 

Ms Otto was married to Mr Davies for four years prior to his disappearance and the couple had been in a relationship for 20 years. 

Mr Davies had known Mr Purkiss for 10 years and regarded him as his "best mate".

Mr Davies' body was found by police wrapped in a blue tarp in a shallow grave on a property at Levendale in June 2017, just over a week after Ms Otto had reported Mr Davies missing. 

Mr Davies was shot twice at close range, in the head and in the back, an autopsy found. 

Crown prosecutor Madeleine Wilson said the state's case was that Mr Purkiss and Ms Otto colluded to kill Mr Davies.

Ms Wilson alleged Mr Purkiss committed the murder as part of an agreement with Ms Otto, making her equally responsible for Mr Davies' murder. 

"Together they perpetrated numerous lies to deflect attention away from themselves," Ms Wilson said.

The court heard Ms Otto and Mr Purkiss were "very close" and were in an intimate relationship which ended in 2016. 

Ms Wilson alleged Mr Purkiss offered to help Ms Otto leave her relationship with Mr Davies and both accused became increasingly resentful towards Mr Davies in the time leading up to his disappearance. 

Lawyer Alan Hensley, representing Mr Purkiss, asked the jury to keep in mind that evidence against the accused was circumstantial. 

"There is no direct evidence that Mr Purkiss is responsible for the death of Mr Davies," Mr Hensley said. 

"Mr Purkiss lost a friend that night - he didn't kill one." 

Ms Otto wiped back tears in the dock as the trial's first witness, her cousin and co-worker Marissa Brown, was questioned in the witness box. 

Ms Brown said she and Ms Otto were "reasonably close" and worked together at The One Stop Shed Shop in Mornington in May 2017 when Mr Davies went missing. 

About 60 witnesses are expected to be called to give evidence during the trial.

Chief Justice Alan Blow told the jury to expect a trial lasting four to six weeks. 

"This will be a long trial by Tasmanian standards," Chief Justice Blow said.