Okay, firstly I would like to say that the person who actually pushed Ian off the bell tower on the set is not the actual actor of the character who pushed Ian off. It was either a stunt man or just a extra (:
Right then, let's get on with the theory!
It is easy to see that Jason always go in and out of Rosewood a lot. These are the episodes of his disappearance and reappearance.
Jason is first seen in the episode "Please do talk about me when I'm gone". He comes back with a clean image after everyone's last seeing was when he was abusing substances and alcohol. He left after the memorial when he gives the girls Ali's bracelet.
He then came back again in "If at first you don't succeed, Lie, Lie again". He left that same episode.
He then returns AGAIN early in Season 2 (Didn't get the exact episode). He was involved in Aria's storyline where she thought she had feeling for him and they kissed, she had dreams about him, blah blah blah. Jason didn't leave in the first half of Season 2.
Between the first half of Season 2 and the second half they had the episode "The First Secret". Also known as the Halloween episode.
When we come back, it is revealed in the episode "A hot piece of A" that Jason had yet again left Rosewood for a month. He later comes back in "The Naked Truth".
So Jason was apparently away from Rosewood in the last episodes of Season 1, including the last episode which features the episode we are going to theorise about, "For whom the bells toll". Which is one reason why I think that it his him, it's unexpected because everyone thought he wasn't at Rosewood at the time.
We all know Jason was part of the N.A.T. club from Ian's yearbook. But when Ian filmed the N.A.T meeting Jason wasn't present. Jason said that he was high that whole summer including the day that Ali went missing, that N.A.T club meeting was filmed the day Ali went missing. Later, it was revealed that Jason and Ian were friends (Obviously due to them both being in the club), and they got high together. So why was Ian there in Ali's room and not in Jason's room getting high. Did Ian quit drugs or did Jason quit the N.A.T club? That could be one of Jason's motives.
Another of Jason's motives for pushing Ian off and saving Spencer is because Jason already knew the Spencer was his half sister, even though Spencer didn't at the time. I know this because, Ian was always asking for Spencer's Dad and having private conversations. And he knew before Spencer as Spencer asked him and he said "How did you find out". That is another motive because he would want to save his half sister "Spencer".
You might ask how would Jason know they were in the bell tower. Well, it looks like Ian was planning meeting Spencer in the bell tower, secrets come out. And as Jason was in the N.A.T club he knows Ian personally, and by being in the N.A.T club he knows how to sneak around without being seen.
We all know that if Jason killed Ian, he would be the one to move the body. As Jason was in the N.A.T club, I doubt he is a A team member as well, so Mona can't have moved the body. But Mona does come into this soon. Wait for it. We all know when Jason finally came back "Apparently when he first came back", he was suspicious. There was a scene with a dog sniffing the ground with a green bag/cover over. If Jason did push Ian off, he must have buried the body there. Very suspicious looking and they wouldn't have put the dog sniffing the ground in if it didn't have a purpose.
Now where does Mona come into all of this? We all now that the A team is everywhere, they know everyone's secrets. And Jason's secrets are no different. I'm guessing that Mona set the dog there to sniff the ground and the body. Why though? Is it because she pushed Ian off and is trying to frame Jason. That's the obvious reason. But maybe the real reason she got the dog was because she knew that Jason done it.
I don't think Jason put the body out though and wrote the note. I haven't figured that out yet but we know Garrett and Jenna know who and how Ali was murdered, and they either done it or they are covering for someone. They probably wrote the fake suicide note but who put the body there in the first place? Did Jason? Did Mona? Or did Jenna and Garrett. There are so many questions to be answered with the disappearance of Ian and Season is the answer (:
This is just a theory. And it is my theory that I wrote so if you would like to share it on your blog or page, you need to put my name somewhere as the original writer. Thanks for understanding! (C).
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