SA dad whose gun killed three walks free

The father of a mentally-ill man who killed three neighbours in an Adelaide shooting spree has been found not guilty of firearms offences.

Guiseppe Corbo, 73, had denied three charges including failing to keep a firearm secured, with his lawyer submitting that he kept his guns in a locked safe and his ammunition in a separate locked safe.

Police had argued he unlawfully failed to keep the keys to his gun safe away from his son, Donato Corbo, who shot dead three members of a family in Hectorville in Adelaide in April 2011.

He also wounded two other people, including a police officer investigating the incident, but was found to be not guilty of all charges by reason of mental incompetence.

He will spend the rest of his life in mental health detention.

On Tuesday in Holden Hill Magistrates Court, magistrate Jayanthi McGrath dismissed the three charges.

Last year another magistrate threw out manslaughter charges against the father.

In the firearms hearing, the prosecution alleged the safe keys were in a place known by the son and therefore his father did not "do enough" to secure the items.

But the father's lawyer, Gilbert Aitkin, said the shootings were committed by a mentally-ill person who did not know the difference between right and wrong.

He alleged police were "intent on this case running to trial" claiming that the son's actions "somehow sheets home" to his client, who had complied with firearms legislation.