Theodicy is the branch of Christian theology concerned with defending the attributes of God (especially his absolute goodness) against objections resulting from physical and moral evil.
A common argument in the tradition of theodicy that I have heard Christians use is that physical and moral evil is the result of Adam and Eve's free will choice to sin by eating of the tree of the knowledge of good and evil, that this tied God's hands, so to speak, in preventing evil.
These Christians never stop, though, to consider the true implications of the doctrine of God's omniscience. According to the doctrine of Divine omniscience God has absolute knowledge of everything, past, present, and future, that he sees infallibly all of time and space simultaneously. But what does this imply ? It clearly implies that God always knew, even before creating mankind, that he would plant the tree of the knowledge of good and evil in the garden of Eden, and he always knew Adam and Eve would choose to sin. Yet God set his plan in motion anyway, knowing all the misery and woe it would result in down through the ages. What this basically means is that God cannot be absolved of the responsibility of evil in the world. God has no needs or desires, he's supposed to be perfect. He didn't need to create anything. He has self-satisfaction and self-fulfillment all within himself. So even the fact of creating shows that God cannot logically be perfect and choose to create something, which no matter how you look at it, implies a need or desire in God.
So, if the Christian God did exist, the responsibility of evil in the world rests squarely on his metaphorical shoulders.