In 1996 a lone gunman entered a classroom in Dunblane, Scotland.
David Barnes
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And the same thing happened after the Dunblane inspired massacre at Port Arthur in Australia in 1996.

The Australian government enacted stricter gun laws and there have been 3 shooting sprees since. That’s 3 in 19 years. Only one of them was someone randomly shooting people (In 2002, 6 years after Port Arthur), the other two seem to have been a domestic dispute and a row between neighbors that got out of hand.