If god can prevent evil, why does he allow it?

bear in mind its not always a matter of someone acting on there free will. such as it is the free will of a killer to kill (although it is against the will of the victim to be killed) but what about freak accidents, such as a fire starting from non-arsen related causes, carbon monoxide, natural disasters, and often these things happen to good (and often devoutly religious) people? in these cases the 'bad' people can die just a brutally as the 'good' people, why doesnt god intervene in these cases, but intervens to perform miracles or give strength?