The comments from Law Society of Tasmania president Anthony Mihal came after Thursday's not guilty verdict at the double murder trial of Nicolau Fransisco Soares.

Mr Soares, 28, who suffers schizophrenia, killed his mother Dr Delys Weston and step- father Professor Gavin Mooney but was found not guilty on the basis of mental illness.

In early 2013 William John Christopher McFardzean Foran was also acquitted over the murder of his mother at Newnham on the basis of mental illness.

Mr Foran had been diagnosed with schizophrenia.

In both trials the prosecution joined with the defence in calling for a verdict of not guilty by way of insanity.

Like the Foran case, the family of Mr Soares had to endure the terrible circumstances of watching an unwell relative on trial for killing a loved one.

Currently, if the state wants to put somebody in a secure mental health facility, it has to prove the person committed what would otherwise be a crime.

However, after two such trials in a little over a year questions surrounding a better alternative are being asked.

"There is merit in considering a change to the criminal code to allow a judge alone to hear trials where there is no issue between the accused and the prosecution that the accused should be found not guilty by reason of insanity and it is in the public interest to do so," Mr Mihal said yesterday.

The society's representative for criminal law in the North, Evan Hughes, said jury trials could sometimes become farcical when mental illness wasn't in dispute.

"My personal view has been for a very long time that we should have had the ability to go to trial judge-alone for quite some time.

"And the law society's position is it definitely has to be looked at,' he said.'

However, Mr Mihal stressed judge-alone trials should only be explored within a narrow framework.

"Maintaining public confidence in the justice system is best served by having juries as the principal trier of fact in all criminal matters, including those in which the defence of insanity is raised."