I started this theory with a few things on my mind:
1. It is probably Sarah Harvey in that grave (but I’m not 100% sure).
2. Mona HAD to be involved in the killing and burying of that girl (either it’s Sarah or someone else) because she wanted to make sure everyone thought Alison was dead and she had Ali’s clothes from that night.
3. The girls were totally drugged the night Alison left.
4. We were told Spencer came back to the barn after she fought with Alison and went back to sleep… But from the pilot we know that she was back outside and when the girls woke up looking for Ali, Spencer says “she’s gone, I think I heard her scream” - meaning that even though Ali saw the girls sleeping, that wasn’t the end of it for them.
5. Emily had a flashback while going through hypnotherapy with Dr. Sullivan that showed her with a shovel, about to beat Alison, who is screaming with terror. She later thinks it’s a memory from the other night she was drugged and was found in front of Ali’s empty grave, but I think that memory was clashed with a memory from the night Ali disappeared.
6. It’s really easy to drug these girls and while they’re under the influence, get them to do something they will never remember later on. I think 3X01, when Emily is drugged and does a whole bunch of things she doesn’t even remember later (being with Paige, getting picked up by Jenna and also being used by A at the graveyard and still having no idea how she got there) - this is all a major clue that in PLL land, this can happen to these girls and maybe even already happened before.
So, this is my theory:
The very first text that the girls received together from A (Mona) was:
“I’m still here, bitches. And I know everything. -A”
Let’s take a look at that text. They got it after Alison’s funeral, and right after Wilden talked to them and let them know that Ali’s case is no longer a missing person’s case but a murder. The girls look very shaken by this and even more when they get the text.
But what is Mona saying? “I’m still here” - Who is? I remember watching PLL for the first time and thinking, well it’s obviously Alison who is still alive that is sending them this text, because it’s signed ‘A’ for Alison and she wanted them to know that she’s not really dead but 'still here’. But now I’m thinking… We know it was Mona who sent that text. She is trying to say, “Alison is dead, but I’M still here.” She is making sure they know that even though Alison supposedly went to the grave with their secrets, someone else is STILL there and “knows everything”. But what does Mona know? So, of course, it could mean all their little secrets (which she later uses to blackmail and torture them with) but I can’t help but recall another hunch that I had when I first watched the show, and that is how this text sounded so much like “I know what you did last summer”. What does Mona know? What did these girls do? What’s the ultimate secret, the biggest thing they’re guilty of?
Well, I think the PLL’s were the ones who killed that girl. It could either be Sarah Harvey, or someone else, but either way I think it was all four - Emily, Aria, Spencer and Hanna - who were involved in the murder and burying. How did this happen? Well, let’s see.
We know that they were all drugged by Alison that night. SO drugged that they all fell asleep, while she was watching them and waiting for a text from A. We know Spencer came back to the barn after their fight, and in 4X24 we see a flashback scene where they’re all sleeping together. However, in the pilot we have the scene where they all wake up, and Spencer is already outside of the barn (meaning, she definitely was awake again) and if you check out the little details and differences between the two scenes, it looks like the other girls were awake as well, after Alison left, and only later went back to sleep:
Of course, it could be a mistake by the props department on the show… but I don’t think so. They made a lot of effort in 4X24 recreating that scene with the same music, cups, candles, Aria’s pig and all… So why not the blanket? I think it’s a clue, showing that they didn’t sleep from the moment Ali left till the moment we see them wake up, rather they woke up in the middle, did something they later forgot, and went back to sleep.
It was a friggin LONG night, that night. We saw Ali get a bunch of 'errands’ done and come back to the barn to make sure they were asleep, and then leave, get hit and buried alive and then escape…all in one night, and it’s still dark when Mona picks her up and takes her to the motel. It’s still dark when the girls wake up and Spencer says that Alison is gone. It’s a really, really long night. So, what happened between the moment Alison left the barn and was hit and buried by her mother and the moment the girls wake up and Spencer says she’s gone?
Well, I think they were all still sleeping while Alison was pulled out by Mrs. Grunwald. She then left her car, only to be picked up by Mona, who convinced her to fake her death. Mona was willing to do everything in order to make this happen, she was helping the person she hated the most, just in order to get rid of her. We see Mona put Alison to sleep and go over to her 'A lair’ next door. Her night was just beginning.
She had access to Alison’s clothes, probably gave her something else to sleep in (we don’t see this, but I’m assuming this is how Ali’s clothes were found on the body) - before Mona went and bought her new clothes in the morning for the Vivian disguise, it was still the middle of the night and Mona took the yellow top and pants and left to make sure that THERE WAS A DEAD BODY FOR PEOPLE TO IDENTIFY AS ALISON. How would her plan of making Ali disappear and assumed dead work, if there was no body to be found? Mona was in charge of finding a replacement. However, I don’t think she did this alone.
Either Mona, or a different person who was helping her (could be: Cece/Wren/Melissa/Wilden/Jason/Avery), or both Mona and this other person - went back to the place where Alison was buried alive, with the clothes that Mona took from Ali. Then, the four PLL’s either woke up or were awoken by Mona and together they killed and buried Sarah Harvey. How they got Sarah Harvey there and why it was specifically her that was killed is a different theory which I’ll write about later, but what I’m focusing on now is how the four PLL’s are involved in this murder.
Remember Emily’s session with Dr. Sullivan, who was trying to help her after the whole Nate/Lyndon thing? Dr. Sullivan wanted Emily to go back to the night she killed him, but Emily’s mind took her to a different night. In the flashback, there is a clear mix up between Alison’s yard where her body was found and the graveyard where Emily was found in 3X01.
Then, in Emily’s mind, we see her holding a shovel and scaring the living sh*t out of Alison… She is wearing the same clothes she had on the night Ali went missing and it looks like she isn’t totally in her right mind. I mean, have you ever seen Emily with those kind of crazy eyes??? This is what Ali was yelling:
“We shouldn’t be here… This is bad, we shouldn’t be doing this! You have to stop! What do you think you’re doing? You can’t do this! STOP!”
Later that episode, Emily remembers that it was actually what she herself was yelling, at the graveyard, when A was digging up the body. Even though Emily was recalling the graveyard from 3X01, the rest of that flashback was pretty gruesome and maybe the biggest clue ever given on this show about what happened that night. She simply dismisses it as a nightmare combined with a memory from the graveyard and then the rest of the girls assure her that she didn’t hurt Alison… But I think it was an actual memory.
We now know it wasn’t Alison in that memory, because she told the girls what she did that night and none of this was mentioned… so could it have been a mistake by Emily’s mind trying to fill in the gaps and in reality, instead of Ali it was actually Sarah Harvey?
What I’m getting from all of this is: Emily was awake that night, drugged, after Ali had already been saved by Mrs. Grunwald and long gone… and she was really holding that shovel and was with this screaming girl. However, Emily wasn’t actually alone with the shovel and the girl, that’s just the only thing her memory allowed her to recall. I think she was there with the rest of the PLL’s (all drugged and woken up by Mona) and also with whoever was helping Mona and got Sarah Harvey there that night. We hear Sarah screaming for her life, it sounds like it’s not just one person who is doing this to her (Also from Emily’s flashback, it seems like she could have just ran away or fought back… Maybe she was held down by the rest of them, only Emily can’t recall that because it’s deeply suppressed and she was very drugged). So, the girls were taken full advantage of and were brainwashed by Mona to hold this girl down, kill her and bury her (or maybe the person who was helping Mona was really close to them and convinced them to do this while they were drugged).
There is no other explanation I can find for these images in Emily’s head. She was wearing those same clothes, she was drugged and totally out of her mind, it sounded like she wasn’t alone in doing this and it was obviously a combination of what she remembered from the night Ali left and the other night at the graveyard. She and the other girls were totally involved in this murder.
I have always believed that the biggest twist on PLL would be that the 4 protagonists we all love and adore would end up being guilty and deserving of the torture that they’ve been through. Of course, it wouldn’t make sense if they were aware of this and just lying (to each other as well? nope), but it would make sense if they all were drugged, didn’t do it on purpose but were used and brainwashed to do this, and suppressed it and could never recall it (unless they went through hypnotherapy like Emily). It’s also debatable what they’re guilty of - maybe they didn’t actually kill the girl but witnessed it / maybe they witnessed the murder and helped bury her / maybe they were convinced to actually kill and bury her / maybe it wasn’t all four girls, it could be just Emily and Spencer or Emily and Hanna or Emily and Aria (remember in 4X01 the whole thing with the little girls and the dolls that resembled the PLL’s and Mona - one of them said, “Not fair, Aria! It was Emily’s idea!” this could be a hint to something Aria and Emily did… maybe it was this. Could this be what Aria’s nightmares were about? Is there some part of her mind that remembers this, maybe her subconscious when she’s dreaming, and maybe Ezra figured this out while they were together?) But either way, I’m sure Emily was involved because of THAT FLASHBACK! (and once again, 3X01 was a clue that it’s easy to drug her and make her do things she won’t remember). It’s really a twist when the person least expected, like Em, has the scariest skeletons in her closet. Still, I’m pretty certain that if it was her, she didn’t do it alone. I think all four girls are guilty (because they were all drugged and so I think they were all involved) and like Ali said, they all remember more about that night than they think.
So, Mona knows this because she helped do it (providing the clothes and making sure a body was found and Ali was assumed dead) and she also realizes that the girls don’t remember this, but she is probably afraid that they’ll recall it somehow. She wants to keep it a secret, because she was involved in the murder as well. I think Uber A is either whoever helped Mona do this and has some sort of connection to the girls or someone connected to Sarah Harvey/or whoever the dead girl is… I am pretty sure Alison has no clue about this and the only other people who know are probably Cece, Melissa, Wilden. I also think Wren found out about this from Melissa (but she might not know he found out) and also Jenna could have found out once she got her sight back.
Once again, I am certain that the girls don’t remember doing this and that they had no intentions to do this, they were just drugged and forced to take part. They ARE, however, considered guilty (especially if you ask Uber A) and I think that’s the biggest secret of Pretty Little Liars. It’s why the focus of the show is on them and also on Mona. We are supposed to relate to them only to discover that the worst secret, the worst lie, is about them. We might even end up on Uber A’s side… After all, Marlene said that is her favorite character :)