Last night’s episode of Pretty Little Liars (Season 4, Episode 8: “The Guilty Girl’s Handbook”) ended with a shocker when Mona (Janel Parrish) walked into the police station and confessed to killing Detective Wilden. Mona’s motives are always in question, but we can’t help but speculate over what they might be. Why did Mona confess to Wilden’s murder?

To prove herself to Hanna

In the Season 4 premiere, Mona insists again and again to Hanna that she really was her best friend and she really did love her. We can’t fault Hanna for doubting Mona after everything her “BFF” put her through as the original “A,” but we do wonder if Mona’s actions in last night’s ep were an attempt at the old adage “actions speak louder than words.” Is Mona trying to prove to Hanna once-and-for-all that she really cares about her, and would do anything for her? If so, Mona really doesn’t do anything halfway.

She actually did kill Wilden

As pointed out by the Liars earlier in the season, Mona’s movement are unaccounted for in the night/early morning of Wilden’s death. Mona has proven herself to be capable of hurting others, and she has plenty to hide. Could she have actually killed Wilden? She was able to easily recall details about Wilden’s murder while coaching Hanna in her confession. Was that because she actually did it? If so it, it’s hard to imagine that she would turn herself in out of pure guilt, but stranger things have happened in Rosewood.

She’s protecting someone else

Even if Mona didn’t commit the murder, it’s possible that she knows who did. In turning herself in, could she be covering for someone else (i.e. Cece or Alison)? Perhaps the Liars were getting too close to uncovering the truth about Wilden’s death and Mona confessed in in an attempt to stop their efforts. Maybe Mona thinks that if the Liars believe that Mona really was the one to kill Wilden and no longer have the impetus of getting Ashley Marin out of jail, then they will stop digging (yeah, right).

Why do you think Mona confessed to killing Wilden? Share your theories in the comments below!

Catch the next episode of Pretty Little Liars on Tuesday, August 6, 2013 at 8 p.m. ET/PT on ABC Family.