Man found not guilty of son's murder

An Adelaide man has been found not guilty of the stabbing murder of his young son because of mental incompetence with his wife telling the Supreme Court that her life has been shattered.

David Janzow, 38, was alleged to have killed his four-year-old son Luca in July last year.

The Supreme Court ruled on Monday that the objective elements of the offence had been proved but that Janzow was mentally incompetent at the time.

He will be held in a secure mental health facility with Justice John Sulan setting a limiting term of life.

In an emotional victim impact statement read to the court the boy's mother, Julia Trinne, described him as a special soul, a cheeky, clever and creative boy.

"He had an inner wisdom far beyond his years," she said.

Ms Trinne said the killing had left her "utterly and incomprehensibly broken" and wishing that her husband had taken her instead.

"I know what it's like to fall to my knees not knowing if I will be able to get up," Ms Trinne said.

"A living nightmare does not come close to what I have been going through."

But she also said she had loved her husband of 11 years and hoped the death of her son would bring attention to issues of mental health and the struggle people battling a mental illness faced.

She said her husband had suffered for some time and then became acutely unwell quickly.

There was no warning ahead of his actions and no suggestion any of her family were in danger, Ms Trinne told the court.