The mystery of Iniquity.
Evil is in this world as a result of man’s free will. We live in a fallen world - we are pilgrims on a journey - heaven is our goal, and in heaven God allows no evil.
Mankind is free to choose good or evil. Otherwise we would be ants marching mindlessly to and fro on the earth. God gave us intellect, reason and the power of choice; that is the part of us that is made in His image - the part that can think and choose. Man’s evil choices can ultimately affect the innocent - look at abortion - however as stated before, we live in a fallen world - the evil will be gone when those of us who make it get to heaven, where nothing imperfect is allowed as it says in the Book of the Apocaplypse.
Hitler chose evil; the rescuers chose good.