Who killed Alison in Pretty Little Liars?

Answer 1

Book Alison killed Alison. Alison had a identical twin sister, Courtney, who was in a mental facility as she was very jealous of her twin and attempted to drown her. Nobody outside of the family knew about Courtney after they moved to Rosewood. Courtney wanted Alison's life and when visiting her family during the weekends (where she was forced to stay inside). However, one weekend she left her house during the Time Capsule competition and she met Spencer, Aria, Emily, and Hanna when they all meet in her backyard to steal her Time Capsule Flag. Courtney pretended to be Alison and eventually made friends with the four girls - who believed her to be Alison. As they were not Alison's current friends they didn't notice any different. Courtney also managed to convince her parents that she was Alison which meant the real Alison was sent to the mental facility in place of Courtney. The real Alison wasn't happy and killed her twin sister, Courtney.

TV Series However, in the TV series, Ian admitted to killing Alison because she had his videos from when he stalked the girls and Jenna. However it is later revealed that he was murdered and it was made to look like a suicide with a fake note claiming he killed Alison. It had not been revealed who really killed her.
Spencer,Hanna,Emily and Aria suspect it is Ian.
Alison never died she had a twin sister named courtney alison killed courtney for stelling her life they swithed places
Nobody killed Alison but her twin sister , Courtney, was killed by Alison . Courtney was pretending to be Alison and got her sister ( the normal one ) sent to rehab. So that's why Alison killed her secret twin sister.
A ;)