How do firemen know the cause of a fire after everything has burnt down?

Question

Often times you hear about the cause of a fire being a cigarette for example. However, isn’t the cigarette already long gone after the house/forrest/etc. has burnt down? How is it still possible find out what started the fire?

In: 567

Answer 1

I was once told newspaper is an effective accelerant that burns up entirely, unlike petroleum based alternatives