Australia used to have lax gun laws. But then in 1996, the mass shooting at Port Arthur - in which 35 people were murdered and 23 wounded - sent such shockwaves through the country that 643,000 weapons were willingly handed over by citizens as part of a "buy-back" scheme initiated by then Prime Minister, John Howard.

Australia now has strict gun control laws, particularly as regards semi-automatic and pump-action firearms.

No other nation on the planet has the USA's problem with mass shooters.