To answer this question, we must first ask ourselves, "Who is really responsible for sin?" Once we unlock the answer to this question, we may begin to discover the party responsible for the evil in the world.
We can tell that men do not obey the moral or natural law as they ought. It does not quite represent what philosophers call self-evident truth, but it comes quite close. Crime, immorality, and twisted desires abound in our society, and something seems desperately wrong with man's nature.
The sin of man is ultimately responsible for most of the evil that we see. Crime, hatred, war, several diseases, and difficult economic times are all brought about by man and not by God or satan. However, some of the evil in the world can be tied back to satan (That is if you accept the biblical account of sin, which we will assume you do for the purpose of argument). Satan causes Adam and Eve to sin and in so doing they transgress a moral law and reap the consequences (Death, sin nature, and diseases.)
What about the natural disasters? They are a part of the curse. One might argue that because God cursed Adam and Eve, that he is responsible. But he only carried out the punishment that he told them beforehand he would carry out. Ultimately, we ought not to hold a judge accountable for a prisoner's sentence because without the prisoner's misdeed, there would have been no sentence.
In the end, It is man's sinful nature that causes most if not all of the evil in this world.