Okay after watching the PLL season finale tonight, this is what I believe to be true. Allison got hit by Jason the night she went missing. Jason was drunk that night and must have mistaken Ali for CeCe since they were wearing similar clothing. Jason must have been still upset about the breakup with CeCe, perhaps even angry enough to hit her. Mrs.D gasps at the sight of her son hitting Ali. She runs out and buries Ali (thinking she was dead) in order to protect Jason from going to jail. This makes sense because Ali overheard her saying “What have you done?” over and over again. Mrs.Grunwald then pulled her out and saved her. Now, that being said, Mrs.D must have put the blame on Spencer and told the Hastings family that she was the one who killed Ali. Somehow, they were able to come to an agreement and would keep things quiet. So when the Hastings family were at the police station being questioned, Peter Hasting was getting worried the police would put the pieces together and discover that Spencer killed “Ali”. However, Melissa Hasting whispers into her father’s ear that irked him. I believe Melissa told her father who killed the girl who was mistaken for Ali to relieve him from the stress he had thinking it was his own daughter. This leads me to believe that Ian was the one who truly killed the girl who he mistaken for Ali, since they looked similar. So when he was at the Bell Tower with Spencer, he was shocked to see Ali there since he thought he killed her. Moreover, on the night that Ali got hit over the head, Sarah Harvey(the girl who actually died and is in the grave) was killed because A) she was either mistaken for Ali or B) she was mistaken for CeCe. Point is, someone wanted to kill both Ali and CeCe. Most likely, this person thought they were killing Ali, since Ali had so much blackmail on people. Especially everyone that had to do with the NAT club since they would go to prison if they were ever exposed. I also have a feeling Peter Hasting was the one who “killed” and buried Mrs.D after realizing she lied about Spencer being the killer. Lastly, if you recall the shirt Mrs.Marin pulls out of a shopping bag in Ali’s room in the last episode..CeCe is wearing the same top in this episode. This could only mean one thing. Mrs. D is protecting CeCe. The question is why? Perhaps CeCe is a niece? These are just a few theories I have come up with. But who is A? I still can’t put my finger on it.