Notice...all of those shootings happened after the confiscation.....and there are the others......the only thing keeping them from being worse was that the person using the gun didn't decide to shoot more people...since he already had the illegal gun...
What I noticed was the most were domestic, drug or gang related. That's what i noticed. Not on the same scale as Port Arthur, nor were they a random act. The victims were known and targeted with most. Aurora, Sandy Hook and Virginia Tech were the result of whackos going bat shit. IOW, you're comparing apples and oranges.
Also, just as an FYI I posted a similar link on another thread that showed up until the end of Sept this year the US had had more than 300 instances this year alone. You've posted 25 instances over 18 years in Australia. About 1.3 a year. The US is at 300+ and counting for this year alone...