How Ordinary People Become Evil Beings

I am looking at how ordinary people can become evil and be responsible for committing horrendous crimes.

What makes normal people do bad things?
How can moral people be seduced to act immorally?
Where is the line separating good from evil?
How does the Chain of Command Responsibility play a role in making people commit crimes? How does the concept of administrative evil” influence others?
If everyone is capable of being persuaded to commit crimes against one another, is anyone really innocent or is everyone guilty in some aspect, some more than others?
What happens to people when they resist the system and refuse to follow orders to commit crimes against one another? What are some examples of people in history refusing orders to do so?