Creating an "evil" character takes time and effort.
First, you must define evil. So let's start with that. What is evil?
Obviously, evil is the opposite of good. That isn't enough though, to make the leap from "He's the bad guy" to "He's evil incarnate" you have to draw it out.
For instance: Adam was a strange and disturbing child. He spent long hours using a magnifing glass to roast ants.
Is Adam evil? No, Adam is naughty and a very rotten little boy, but not evil.
Now look at John:
John stared into the distance, not seeing anything around him. All sight, smell and sound had fled from him as he focused only on the sensation of the thrashing kitten whose head was now fully submerged.
The sensations not longer satisfied him, there must be something else, something that could fight longer, something that would gaze at him with understanding as the light faded from it's eyes. But what?
Now is John evil?
You be the judge.
Creating an evil character is taking everthing that terrifies you and rolling it into one person. If you look at your creation and shiver; then you've probably succeeded.