Since the day that Cain killed his brother Able there have been people who do evil things to other people. History is full of horrific misdeeds committed on unsuspecting populations. Hitler was not the first nor was he the last person to try and kill off whole groups of people.
My religion, as most religions, teaches that such persons will face eternal punishment for such evil deeds. Society also provides punishment for evil deeds if the perpetrator gets caught. The ancient Jewish law called for an eye for an eye and a tooth for a tooth. Some countries cut off the hand of a thief and even will kill one who murders another. Tough penalties are often seen as a deterrent to future crimes. It deters future crimes by that person but other evil people will still do evil things.
Most of us refrain from doing evil simply because we have a deep seated desire to be good. About ten percent of us are not bothered by a desire to be good and the only thing that keeps us in check is the fear of getting caught. There are those few who think that they will get away with doing evil things. They can not conceive of getting caught or that they are so important or powerful that it won’t matter.
We can never totally stop evil people from doing evil. Always there will be the con artist that tries to seal our money, an angry person who is willing to kill another person or a sick leader who wants to start a war. Society needs to try to stop them but always there will be evil ones who will find a way to destroy our peace and peace of mind. Our personal response needs to be rooted in our faith so that we have the internal fortitude to recover spiritually from such actions every time they occur.