This is not MEANT to be a spoiler, but in the event it turns out to be, please skip this re The Killing.
Early on I felt I could not bear to go through all the episodes and not know who done it. I always read the last chapters of a mystery before I read the whole thing. Living with suspense is not one of my virtues.
So I went on line and google searched the Danish version. It had been my understanding that the American one was the same, only 13 episodes instead of 20 and a different country and city.
In the Danish one, Forbrydelsen, which won the BAFTA award, beating out all of the British and American competition, the assistant to Rosie's father is the killer. Do you remember in the very first episode where he is quite nasty to some Middle Easterners they do a job of moving for, and if I remember correctly, he refers to them as "ragheads?" Well, apparently he thought Rosie was dating one and that curdled his senses and made him murderous. At least, that is how I read the plot outline I found of the Danish Forbrydelsen, and I watched The Killing for weeks thinking I knew who the killer was.
Then, a couple of weeks ago, I read to my great distress that the writers had CHANGED the killer in the American version just so no one would know until the last episode. If that is true, I know no more than you do as to who it is. The 12th episode seemed to end with the finger pointing to the city councilman who is running for the job of Mayor.