To try and understand these answers, I turned to the Catechism to see what the church really believes in “evil” and how it answers the question of why God allows evil to happen.
Evil Comes from Sin
Whether you believe it in or not, evil exists in our world. There are those who may try to explain away an evil act as a developmental flaw, a psychological weakness, a mistake, or the consequence of an inadequate social structure, etc., but evil is a direct consequence of sin and it comes from humanity’s rejection of God and opposition to Him. Sin is an abuse of the freedom that God gives to created persons so that they are capable of loving him and loving one another. (CCC 386-387)
The source of all sin can be found at the beginning of the history of man, with the first original choice to turn away from God, and sin has marked the whole of our human history. All sin, no matter how small, leads us toward evil and away from God.
God is Good, All the Time
However, it is important to realize that God is infinitely good and all his works are good. (CCC 385) He does not do evil and He does not condone evil. He gives us free will to act. He gives us the free will to choose whether we act out of love for Him and thereby for one another, or to shut ourselves off from His love and grace. Unfortunately in our world, there are persons who choose sin, who choose to be separated from love, who choose evil.
When faced with this evil, we also have free will to choose our response. We can harden our hearts with grief and hate or we can seek and find God’s love. For He knows what good may come out of our grief. Only God is able to take evil acts and use them to bring light to darkness. He knows we need help fighting evil and so He sent us a Savior in his son, Jesus, to lead us. Nowhere is this free will and Christ's goodness more evident than in the victim's families choosing to forgive.
The victory that Christ won over sin has given us greater blessing than those which sin had taken from us: “Where sin increased, grace abounded all the more.” Romans 5:20 (CCC 420)