Margaret Anne Otto, of Risdon Vale, and Bradley Scott Purkiss, of Elderslie, are jointly accused with the murder of Ms Otto's husband Dwayne Robert Davies.

Both have pleaded not guilty.

Mr Davies' body was found in a shallow grave at Levendale on June 3, 2017, a week after he was last seen.

The crown alleges the co-accused colluded to kill Mr Davies.

Earlier in the trial, the court heard evidence in the days following Mr Davies' disappearance the pair told friends and family a number of possible alternatives for what may have befallen Mr Davies including he had gone on a drug bender or had committed suicide.

Forensic pathologist Dr Donald Ritchie told the court on Friday Mr Davies died as the result of two close range shotgun wounds, one to each the back and head.

Dr Ritchie conducted an autopsy on Mr Davies' body on June 5, 2017.

The jury was shown pictures taken during the autopsy.

"The round nature of the central wound, with some scalloping on the outside, is characteristic of [being] close range," Dr Ritchie said.

"When I say close range I mean under a metre.

"He would not have survived either of those wounds. Both would have been instantly fatal."

Dr Ritche said although, from the autopsy it could not be determined which wound happened first, it was his opinion Mr Davies was first shot in the back followed by the head.

Forensic toxicologist Neil McLachlan-Troup said Mr Davies' blood underwent a test for alcohol, a comprehensive drug test and an illicit drug test.

Mr Troup said Mr Davies tested higher than average for THC (cannabis) but his blood did not show any evidence of the 150 other drugs screened as part of a comprehensive drug test.

The court heard the tests did not detect synthetic 'designer drugs'.

Mr Troup said Mr Davies' urine tested positive for a small amount of alcohol.

"If this alcohol result had been a bit lower in the urine we would have reported it as not detected," Mr McLachlan-Troup said.

The trial before Chief Justice Alan Blow will enter its fourth week on Monday.