They don't mention Australia, because the murder rate gradually decreased (though it was on a trend down anyway).
Or you can find cherry picked data about how gun related crime falls if you ban guns.
The only reason this debate keeps going is that there's bugger all hard evidence on either side. Sometimes overall crime rates drop. Sometimes they rise. So both sides just cherry pick stats, and call the other side idiots.
If the occasional mass shooting is acceptable, there's no reason to either ban guns or keep them. "Guns cause crime" and "guns stop crime" are both red herrings.
Whether the freedom to have a gun (which won't make you statistically more or less safe) is more important than stopping mass shootings is a value judgement. The statistics are a wash.
I'd say something similar to Australia is a good compromise - allow single-shot long guns (for sport), and ban semis / handguns (unless you have a really good reason). There's also laws about gun safes, safety tests, etc.
The most well-known mass shooting in Australia since guns were banned left three people dead - a shooter with a double-barreled shotgun, and two victims. Australian style laws do a good job keeping mass shootings from causing too much damage.