Gun Control, confiscation and amnesties.

https://ssaa.org.au/assets/news-resources/research/2008-08_the-australian-firearms-buyback-and-its-effect-on-gun-deaths.pdf

Melham pointed The Conversation to “a direct quote from the University of Melbourne’s independent study by Lee and Suardi, 2008”, which states:

… the National Firearms Agreement did not have any large effects on reducing firearm homicide or suicide rates.

Melham added:

Homicides using a firearm were on the decline well before the anomaly of the Port Arthur murders. The Australian Institute of Health and Welfare’s firearm injuries and deaths report 2017 clearly shows that firearm-related deaths began steadily decreasing from 1991, five years before the National Firearms Agreement was introduced.

https://theconversation.com/response-from-the-sporting-shooters-association-of-australia-nsw-for-a-factcheck-qanda-on-gun-buybacks-and-gun-deaths-86052