It took jurors just over an hour to return unanimous not guilty verdicts to two counts of murder against 29-year-old Nicolau Francisco Soares at the Supreme Court in Hobart yesterday.

Mr Soares had been charged with killing Dr Delys Weston and Professor Gavin Mooney at their home in the state's South in December 2012.

Family and friends of Mr Soares huddled together and cried in court as the verdicts were announced, mouthing the words "we love you" to him and thanking jurors as they left the court room.

Speaking outside court afterwards, Alex Soares said the two deaths were a direct result of his brother's untreated mental illness and the failure of the West Australian health system.

Mr Soares said the family watched his brother's health slip away to the point his paranoia and delusions came to dominate him.

He said the family knew Nicolau was vulnerable, that he could not be trusted to take his medication and that he was not taking the drugs in the months leading up to the attacks.

"We were the ones who pleaded with Nic's treating team for an increased level of care," Mr Soares said.

"Despite our parents' unwavering love for our brother and absolute resolve to getting him help, we were ignored and cut out of his treatment.

"How could this have happened?" he said.

Earlier, both the prosecution and defence urged the jury to find Mr Soares not guilty by reason of insanity.

The jury had heard Nicolau Soares had lived with schizophrenia since 2006, with his condition characterised by paranoid beliefs and grandiose delusions.

Evidence was given his symptoms penetrated "almost to the core of his existence" at the time of the attacks.

The court heard he was convinced killing the couple was the only way to avoid readmission to a psychiatric unit, which he believed would prevent him from pursuing a career in the elite ranks of the armed forces.

In her closing address, defence lawyer Rochelle Mainwaring said there was no dispute Mr Soares bludgeoned his mother and step- father to death.

But Ms Mainwaring said her client was unable to understand or appreciate what he was doing was wrong.

"The devastating outcome was, for Mr Soares in his mind, just a means to an end," Ms Mainwaring said.

Crown prosecutor Linda Mason said a verdict of not guilty by insanity was not a soft option.

"As gruesome as the killings were, perhaps they are the best insight you'll ever get into Nicolau Soares's thought processes at the time," Ms Mason said.

Justice David Porter has adjourned the case until July 18 while two mental health reports are prepared.

Mr Soares has been remanded in custody until then.