Who killed Toby’s mom? Who is Charles DiLaurentis? Who Hit Ali? All of these questions and more were answered during the Season 6 summer finale of Pretty Little Liars, but I’ve always been more interested in the mystery that’s inadvertently plagued us nearly since the beginning of the show: Who killed Bethany Young on Pretty Little Liars? Back in Season 4, viewers learned that it wasn’t Alison’s body in the hole in the backyard, but Bethany’s, and we were all like, “Um, who is Bethany anyway?” She was murdered in the DiLaurentis backyard, and while we knew it was Melissa who buried her alive (not knowing it was Bethany or that she was alive), "Game Over, Charles" revealed that Mona hit Bethany with the shovel, leading to her death.
Up until Tuesday night, all we knew about Bethany, besides those few details on her death, was that she was a patient at Radley, she had a close-but-fraught relationship with Jessica DiLaurentis, and she eventually escaped the sanitarium. We never knew how she ended up in Ali's backyard, or who the middleman murderer was — until now — and boy, is her motive a doozy.
Mona was the one who killed Bethany! When Ali was making Mona's life a living hell, Mona had started sending her threats to get her to lay off. One night, Mona was at the DiLaurentis house when she had so much rage built up inside of her that she just went off. As Mona confessed to the liars, "the shovel was right there." She thought it was Ali, but it ended up being Bethany Young in the backyard. Of course it's not like Bethany was an innocent — we also learned in the finale that Bethany killed Toby's mom on the roof of Radley.
