Do you really need 40 kg of potassium nitrate for your hobbyist fireworks though? That amount can blow up a house.
Also if you absolutely can't live without the immature thrill of mixing explosives with your bare hands, at least don't do it in a residential neighborhood.
I see "charged," not "convicted" in that article.
Real world: Innocent until proven guilty.
Internet: Always guilty, because justice doesn't scale.