If we assume they're playing fair, then the Overseer is probably still among us. But...

[Since when have any of the staff members played fair?]

If it's one of the people who went missing, they could be hiding where we can't get at them, too. I asked Judy and she said there is one other place people can vote from, but that door won't unlock until more people are dead. If one of the people who went missing is hiding up there, and voted from there, then...