Arson is a strike. Depending on what burned, a conviction counts as a violent felony that follows a person for life and doubles the sentence on anything that comes after — whether or not anyone was ever hurt. It is also one of the most over-charged offenses in the system, because fire is destructive and prosecutors reason backward from the damage to intent. But arson requires that the fire was set willfully and maliciously. Accidents are not arson. Fires of undetermined origin are not arson. These cases turn on fire-cause-and-origin analysis, and the government's investigators are not infallible — the field's own science has been overturned enough times to convict innocent people and, years later, to exonerate them.