Pretty Little Liars :Theory of Alison's Death?

Tweet

I am totally addicted to this, my mind is twisted thinking who is "A" and who killed Alison Delarentes. Any idea who is "A"? Does "A" have "friends" helping her/him to scare the four ladies? What is your theory? My theory is Alison is not really dead and she has a twin sister(in the prequel episode, Ali was telling a story). I think that Ali's story was real. I think her twin tried to kill Alison so she was send into asylum called Radley Sanitarium. Alis also said that the twin was escape from the center. The dead body they found was not really Alison's body, it's was her twin sister's body. So, what do you think? What's your theory? Can't wait to read yours.