I have never known what to say to people at a time like this but I just re-listened to a very moving non-political speech Joe Biden gave to the TAPS (Tragedy Assistance Program for Survivors of active military personnel killed in action) organization. Having been through the loss of family members himself, he promised that the time would eventually come when the person's memory would "bring a smile to your face before it brought a tear to your eye".
Here is the link in case anyone wants to watch:
http://www.youtube.com/watch?v=GwZ6UfXm410