When writing a Horror story, one must begin with a Monster. The most terrifying of course, are the ones you don't notice, or refuse to notice. The ones right next to you.
"The most dangerous werewolves are the ones that are hairy on the inside."
-- A Company of Wolves
Making a MONSTER
Think, who are the people that walk right up to you every day and you let them?
Now imagine if one of them was a man-slaughtering or even man-eating Monster?
In reality, it happens all the time. They're known as Psychopaths.
Psychopaths cannot be understood in terms of antisocial rearing or development. They are simply morally depraved individuals who represent the "monsters" in our society. They are unstoppable and untreatable predators whose violence is planned, purposeful and emotionless.