To be fair, in an old church like that you're going to have a lot of old, dry wood both on the floor and in the rafters, so it could easily go up like a box of kindling if a small fire broke out. Something has to have started it, though. Could have been Satan?
That said there was a big house fire near me a few months back, went from a small blaze to the roof caving in within 20 minutes. Turned out to be an insurance job by the owners. Think they used a bit too much petrol
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