On the 13th of March 1996 Thomas Hamilton walked into Dunblane primary school in Scotland armed with 4 handguns and enough cartridges of ammunition to kill everyone in the school- and opened fire on the primary 1 class, killing 17 people and seriously injuring several others.
When the parents of the murdered and injured children found out that his guns and ammunition legally owned they decided the laws had to change.
Thanks to their heroic campaigning to this day the Dunblane massacre remains the UK's only school shooting and largest mass shooting.