We know Ali DiLaurentis is a liar, but is she a murderer, too?

Pretty Little Liars isn't afraid to throw major twists our way, which is why we love to dive into the world of crazy fan theories every week to see what the show's smart fanbase has come up with. After all, in a world where Ezra might be "A", anything seems possible, and you never know when an out-there theory will turn out to be 100 percent correct.

This week, we want to highlight a theory that this Tumblr user sums up well: That whoever is buried in Ali's grave (because it's clearly not Ali) was killed by Rosewood's biggest mean girl herself. As twisted as it seems, this theory actually makes a fair amount of sense. Let's run down the reasons why.

Someone is in that grave. While the details on the autopsy report could be faked, it seems unlikely that there was no one in the grave at all, since "A" later stole (and then returned) a body from it. Dead bodies aren't easy to come by, so it's possible that whoever faked Ali's death resorted to murder to make the story seem real.

Was the autopsy faked? Obviously some element of the autopsy report was off, because unless Ali had a twin (another popular theory), the identification of the body as hers was totally off base. However, it's possible that the mode of death was not fudged, in which case it seems even more likely that someone was killed for the exact purpose of covering Ali's escape, since the body in the grave went through similar traumas as Ali, such as being buried alive.  

Ali had a secret to hide. Who would have motive to kill someone and make it seem like the body was Ali's? While we could come up with several theories, Ali is the obvious answer. She's the one in hiding, so she's the one who benefits from the world thinking she's gone.

Is she evil enough to do it? It's hard to tell exactly how twisted Ali is. Before she disappeared she was a bully with a talent for tearing people down, but does that mean she's capable of murder? We're not sure, but it certainly seems within the realm of possibility.

What do you think of this theory — is it possible, or totally crazy? Sound off in the comments below.

Catch the Pretty Little Liars Season 4 winter premiere on Tuesday, January 7, 2013 at 8 p.m. ET on ABC Family.

Rebecca Martin is an Associate Editor at Wetpaint Entertainment and our resident Game of Thrones, Breaking Bad, and genre TV expert. Follow her on Twitter and Google+!