Can God Ground Necessary Moral Truths?

Robert from Canada wrote to Reasonable Faith:
Dear Dr. Craig,

There have been a lot questions recently asked about grounding the existence of morality in God, and I have one as well. The Christian philosopher Richard Swinburne rejects the Moral Argument for God because, he thinks, moral truths are necessarily true, and so the existence of God cannot have an effect on their truth.

He comes to the conclusion that moral truths are necessary because certain events are thought to be morally good or bad; more than that, the moral goodness or badness of an event is inseparable from the state of affairs itself. So, Swinburne claims, there is no possible world in which the exact same things occur as occurred during the holocaust, and in which the holocaust is not morally abominable. It is the same with other events that are considered morally good or bad. There is no possible world in which the event is the same as in the actual world and in which the moral judgement of the event is different than in the actual world. Thus Swinburne concludes that the moral judgement of an event is necessary to the event itself. And this leads naturally to his conclusion that the existence or non-existence of God is irrelevant to the existence of the moral judgement since the moral judgement is necessary given the event.

Swinburne's argument would thus undercut one of the premises to your moral argument. I am a Christian philosophy student at a secular university where many of my professors take a view similar to Swinburne, holding that the objectivity of moral values does not depend on God's existence. I have read and heard your arguments about the absurdity of life without God, and I am currently undecided. What would be your response to Swinburne's argument?

Robert