The Royal Commission investigation will look into the shooter's activities, use of social media and international connections, as well as whether there were inappropriate priority settings in counter-terrorism resources.
The apology is for more than 8,000 cases of sexual misconduct largely committed at religious and state-run institutions responsible for the safety of children.
Australia's longest-running royal commission has been investigating since 2012 how the Catholic Church and other institutions responded to sexual abuse of children in the country over 90 years.
Messages of sexual abuse survivors were released in a book to mark the end of a five-year investigation which heard reports of abuse occuring in more than 4,000 institutions.
An Australian investigation into child sexual abuse learned that between 1980 and 2015, 4,444 people had reported abuse. The average age of victims for girls was 10.5 and 11.5 for boys.
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