How Would You Convince Someone That Evil Exists?

Questions about how to convince someone that evil exists, whether Charlie Kirk’s murder was part of God’s plan, whether that would mean the murderer didn’t have free will, and whether or not God is responsible for that plan.  

• How would you respond to an atheist friend who doesn’t believe evil exists and thinks “evil” actions are done by people who are just trying to get by with the circumstances they’ve been given?
• If God is sovereign and has a plan, then he knew Charlie Kirk would be murdered. But if it was God’s plan, does that mean the murderer didn’t have free will, and is God not responsible for his plan?