Uranium is always falling apart, it's constantly disintegrating. The nucleus is built too large. It seems to have transgressed this invisible kind of limit of nature. In my book I call it a "geological original sin."
How would you expect a detective to solve a murder without using any of today's modern forensic evidence tools? Well, they had to do it somehow -- and in this historical mystery Bernard Cornwell imagines what the task must have been like in Regency England.