The problem you have here is that your conception of this requires the potentially-'evil' to be intelligent - your assumption seems to be that these monkeys are

The problem you have here is that your conception of this requires the potentially-'evil' to be intelligent - your assumption seems to be that these monkeys are smart enough to 'know right from wrong' or some such. But 'evil' is a human concept. I'm not saying some animals aren't capable of having a similar concept, but 'monkey evil' would not be rooted in the human evolution of societies, religious and philosophical traditions, etc. Try this one out: Are humans who kill monkeys for science "evil"? Not to (many) humans. But to monkeys?