At this time of great sorrow, we should look in the mirror and reflect on the sin that rests in our flesh and the flesh of all men that precipitates such evil and hatred.
As a Calvinist, I know that God is in complete control of everything, yet is not the author of sin. He uses sinful men for his divine purposes. He can never be frustrated in His purpose. And that the same God who brought the victims into this world, oversaw every aspect of there passing to the next. That does not mean that God directly caused their death. It does mean that God was not caught asleep at the wheel. May He give us grace to trust in Him and lean not on our own understanding.