Pretty Little Liars is a twisty, turny show that will stop at almost nothing to shock its audience.  At this point, we're not convinced there's any line it won't cross, which is why we like to dive into the world of awesome, crazy fan theories every week. After all, with this show, you never know when the fans are going to get something totally right.

This week, we want to talk about Ian Thomas (Ryan Merriman). More specifically, who killed him. After all, that's a mystery that has yet to be solved, even though it's been a question hanging over the Liars' heads since Season 1.

More specifically than that, we want to highlight the theory this Tumblr user posits: That Alison herself killed Ian. After all, we now know she was alive and kicking when Ian mysteriously died, and as soon as we saw this theory, we thought of a couple reasons it could turn out to be true.

She might have motive. It's pretty much fact that the NAT club was not happy with Ali around the time she disappeared, and we know she and Ian had a complicated relationship, to put it mildly. Was he the one who tried to kill her, prompting her revenge? Or did he try to find her, convinced she wasn't dead? Would Ali kill to keep her secret? At this point, we don't know enough about the person Ali has grown up to be to really say one way or the other.

She has opportunity. Ali certainly had the opportunity to kill Ian. After all, she was alive and in hiding. She basically had all the free time in the world.

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

Find Pretty Little Liars spoilers here.

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+!