Well, one major thing is, we don't know everything the police know. For some reason, they seem convinced LHR, BRS, LB and Stine are all the work of the same guy. I'm guessing they have something solid to base that on, something besides letters and phone calls.
Some suspected Zodiac attacks, like Domningos/Edwards, CJB, Lass, they don't include and it's probably because they can't connect them with the solid evidence they have on the other "known cases".

