I've heard small conspiracies called out to justify mass surveillance. You don't really need mass surveillance of your own citizens unless you are concerned about very small conspiracies. Bigger conspiracies can be uncovered with more traditional detective work.
Freak fires are also not a great example. An arsonist cannot cause hurricane force winds to assist and push a fire through a city. This is effectively an act of God. The time bomb is a better example, though again I would ask for evidence that this was a fairly common event the way mass shootings and similar terrorist attacks have sadly become.
In terms of most kills by a single person one sniper is credited with ~700 kills and a mounted knight in plate was expedition to equal 100 peasants on average so 200+ in exceptional cases seems reasonable especially considering the Spanish conquest of South America where in the 1500's where ~300,000 vs 2000 and the 2000 won with minimal casualties. https://en.m.wikipedia.org/wiki/Spanish_conquest_of_the_Inca...
The fact that something is a convenient and effective narrative for propaganda purposes doesn't mean it is a significant and common threat.
We have also forgotten a lot of this crap. EX: 40 to 81 people killed from a time bomb in 1875. https://en.wikipedia.org/wiki/Alexander_Keith,_Jr. Note, this was for insurance money not terrorists, but I don't think the dead care.
Some historical examples where donations where probably accidental. The Delft Explosion of 1654 killed 100-200 people. In 1769 ~3000 people where killed when a depo @ Bastion of San Nazaro in Brescia was struck by lighting. A lighting also sparked another detonation in 1856 killing ~4,000.