It all makes sense now. Louis Kennedy wasn't killing all those woman. It was Samantha, after Louis locked her in the laundromat and burnt it down, she survived. She must've lost her baby though, with almost being killed losing her child and being terribly burned, she completely snapped...

Feeling bad for Louis, Samantha and the victims of Samantha's insanity, Sara tears up and violently yells

WHY MUST SHIT LIKE THIS HAPPENED IN LIFE?!?!

Sara says as she points the revolver to her head