Lucy Hale may not know who "A" is, but that doesn't mean she doesn't have her theories.

The "Pretty Little Liars" star recently told "Watch What Happens Live" host Andy Cohen that she thinks mysterious baddie "A" is “one of the four main girls" -- which doesn’t rule out her character, Aria. We've had our suspicions about Aria since season one, but is it possible one of the other Liars could be the enigmatic psycho-stalker? We weigh the possibilities, starting with the least likely Liar:

Hanna

Hanna being "A" is highly unlikely. It's not that Hanna isn't smart enough to pull it off -- she is a secret genius, after all -- but Hanna seemed genuinely heartbroken over Mona's "A" reveal, and equally saddened by her death. Not to mention, "A" was the one responsible for sending her mom to jail.

And while Hanna more than anyone has a reason to hate Ali, if there's one thing we know about Hanna, it's that she's incredibly loyal to her friends. So we're putting Hanna at the bottom of our list.

Emily

Emily has always been the detective of the group, and her ace investigative skills could be a sign that she knows how to cover up her tracks. This is an important "A" trait. Em also has the strongest feelings toward Ali -- Ali was her first love -- so that would account for a motive. Plus, Emily was the first Liar to befriend Toby, who we know had connections to the "A" team. That being said, "A" also was responsible for driving a car into Emily's house, and we just don't think Em would put her mom through something like that, especially after she got her fired from the police station. Even though Emily has the motive, we don't think she has the heart to be "A." Now, Spencer on the other hand...

Spencer

Spencer is the perfect "A" suspect: she's smart, conniving, and has a known ruthless streak. That, and she's Ali's biggest threat now that Mona's out of the picture. Spencer briefly joined the "A" Team in season three, but what if she never turned in her “A” Team badge? In the season four summer finale, Mrs. Grunwald implied that one of the Liars couldn’t be trusted. Could that Liar be Spencer? Sure, she seems to head up the “A” hunt, but what if that’s just a ploy? What if she’s the reason “A” is at least always one step ahead of them? Still, Spencer has an alibi to account for where she was at the time of Mona's murder. She had already been arrested for the murder of Bethany Young. So if Spencer didn't commit the murder, who did?

Aria

Maybe it's because her name starts with "A," or maybe it has something to do with her suspicious timing, but Aria has been a fan-favorite “A” suspect since "Pretty Little Liars" began. So much of her storyline is devoted to her relationship with Ezra, which means Aria is often missing when “A” shenanigans go down. That, and when stuff does go down, Aria usually gets off the easiest. And when Mona accused Aria of ditching her in season four, was she upset about getting kicked off Team Liar -- or the "A" Team?

We also have to take into account that Aria has a serious lack of motivation for finding "A." In the most recent episode of "Pretty Little Liars," Aria told Caleb that she wanted to learn how to hack into Oberlin College's admissions files to see if "A" had messed with her transcripts. But what if the plan had been to hand Mona's computer off to one of her "A" Team lackeys all along? Maybe she needed a cover-up just in case Mike was around.

With so much evidence stacked up against Aria, we wouldn't be surprised if the most eccentric Liar also happened to be the evil protagonist at the center of all of the drAma. And the fact that Hale is the only main castmember who doesn't know "A's" identity only further rouses our suspicions.