How Evil To Make Your Villain?

 

When you are creating a villain for your book, how evil do you go? I write with serial killers as my villains and I want them to be as true to life as possible. Nothing in my books is gratuitous everything is there for a reason.

When I am reading a suspense or thriller I want to have an uneasy feeling, while I am reading about the villain in the book. I think it’s necessary to make it tense and foreboding. Making the reader hope they would never run into the types of killers I create.
So if you are writing a cozy mystery the villain will not be as evil or you may not describe his attacks as vividly as I would in my books. Whatever type your villain it is important to have a villain that is believable.
What do you think? How do you like your villains?