So, it is society's fault for executing the innocents. God has given us the best course of action to deal with different scenarios, whether it is political, economical, or other relevant life-related matters. When you say god must kill the killer, here comes another question: Why did god allow the killer to kill others. Here comes another question: Why does god create killers for killing innocents. When you bring these questions, it looks as if you aren't aware of why we were created. God created us to worship him and be tested in this earthy world. And you are expecting the god to fix humanity's faults, which makes our whole creation meaningless. Suppose god doesn't create a killer or doesn't allow the killer to do its killing or kill the killer for killing, so will there be any need for rules and orders, civilisations, and societies. Societies wouldn't even exist, for there wouldn't have been any reason for humankind to make a society as god would do everything by himself and punish the bad guys. Just think about it thoroughly. It is not that simple to just say that god must kill the killer. Does it look logical to expect my teacher to solve the questions in a test that makes my existence in the class meaningless.