A man accused of murdering his twin brother south of Adelaide last year is expected to be found not guilty by reason of mental incompetence.
Lucas Brian Timothy Cawte had been due to stand trial in the Supreme Court over the murder of his brother Jake at a property on Marshall Road at Willunga in March, 2017.
The court had previously heard that Mr Cawte fatally shot his brother in the head, before later turning himself in at the Christies Beach Police Station.
Mr Cawte's lawyer entered a plea of not guilty on his client's behalf in September last year.
On Friday, prosecutors told the Supreme Court they had conceded that the defendant had not been "mentally competent" at the time of his brother's alleged murder.
"I can indicate the director concedes that Mr Cawte was not mentally competent to commit the offences," prosecutors told the court.
Mr Cawte's defence lawyer, Thomas Abbott, asked Justice Nicholson to set a date to find his client "formally not guilty" for that reason, which His Honour agreed to.
Mr Abbott said his client was "in the rehabilitation ward" at James Nash House and was "very stable".
Previously, Mr Cawte's family had described the twins as "best friends".
The matter will return to the Supreme Court next week.
