who tried to kill alison dilaurentis in the show
Alison DiLaurentis After Ian Thomas is pushed down by "A" from the top of a bell tower and his body goes missing, the girls are forced to keep their friendship a secret and to maintain therapy sessions with Dr. Anne Sullivan to discuss about Alison's absence in their lives, a fact that their parents believe to be the reason why the girls are behaving strangely.[16] Days after, through Spencer's sister Melissa Hastings, the girls find Thomas' dead body, accompanied by a suicide letter in which he admits that he killed Alison.[17] Following, the girls continue to be threatened by "A." Garrett Reynolds is arrested for Alison's murder after Jenna Marshall hands the Rosewood Police Department a missing page of Alison's autopsy.[18] The second season ends when Mona Vanderwaal—a Rosewood High student and one of Alison's victims of bullying when she was alive—is revealed as "A."[19]
Pretty Little Liars Set in the small suburban town of Rosewood, Pennsylvania (not far from Philadelphia), the series follows the lives of five girls: Spencer Hastings, Alison DiLaurentis, Aria Montgomery, Hanna Marin and Emily Fields, whose clique falls apart after the leader of the group, Alison, goes missing. One year later, the remaining estranged friends are reunited as they begin receiving messages from a mysterious villain named "A" or "A.D.", who threatens and tortures them for the mistakes they have made before and after Alison was alive. At first, they think it is Alison herself, but after her body is found, the girls realize that someone else is planning on ruining their lives.[2]