Who Is the Witch Killer on 'Once Upon a Time'?

Each season of Once Upon a Time has had its mysteries. In season 7, the mystery of the first half is the usual mystery of who cast the spell, how can they break the curse and everything else that goes along with it. However, the second half is a whole new mystery with a witch killer on the loose. After Victoria's death to wake Lucy up, someone has been going around killing women believed to be part of the witches' cult. And while there have been some suggestions, it's possible there could be a few people who might be the killer.