Our understanding of who did what — if anything — with chemical weapons in Syria is no clearer today than it was a week ago. That's when President Obama said while there is evidence of chemical weapons use in Syria, there is none pointing to who is responsible. For more information, David Greene talks to Gary Samore, former coordinator for weapons of mass destruction at the White House. He is now the executive director of Harvard Kennedy School's Belfer Center for Science and International Affairs.