The Killing

I got crazy addicted to season one of The Killing on AMC.  Remember that red-haired twin on Big Love that married whatshisname's brother?  She's in it.  Season 1 is really good and I almost watched the whole thing in 1 day.  Only (mini-spoilers coming) it was such a drag that they didn't say who the murderer is at the end.  I thought they were totally going to do like a Veronica Mars/new mystery every season sort of thing.  Now it's like... what? The mystery will never be solved?  I can't stand that sort of Lost/Heroes nonsense.  But, what I don't understand, and if you do, please tell me - how can it be that the mayor-candidate is not the killer when he's the one who sent the creepy emails to the high-class hookers?  Too many shows, I'll tell ya', just plan out one great season, then they get renewed, and it's like, oh shit, we have to think up some more ideas?!?!