What is the source of evil in the world?
Man himself
The Lord God said, “Since the man has become like one of us, knowing good and evil, he must not reach out, take from the tree of life, eat, and live forever.”
Genesis 3:22 CSB
Man’s first act of disobedience [sin] resulted man obtaining in the knowledge of evil (he already had the knowledge of good because he knew and walked with God).
Since man was not originally designed to have knowledge of evil, he does not have an adequate defense mechanism to deal with or resist evil. In one sense, evil is like an evading virus which takes over a normally functioning cell and then uses that cell to reproduce itself. Man became a slave to evil.
5 When the Lord saw that human wickedness was widespread on the earth and that every inclination of the human mind was nothing but evil all the time, 6 the Lord regretted that he had made man on the earth, and he was deeply grieved.
Genesis 6:5-6
21 When the Lord smelled the pleasing aroma, he said to himself, “I will never again curse the ground because of human beings, even though the inclination of the human heart is evil from youth onward. And I will never again strike down every living thing as I have done.
Genesis 8:21 CSB
Who is responsible for evil being in the world today?
Man, his original choice opened up man to evil within himself, which he was and is unable to control. Therefore, we see the results in the evil within man acted out in the actions of men in the world.