WASHINGTON, DC - SEPTEMBER 11: (R-L) U.S. President Barack Obama, first lady Michelle Obama, Vice President Joseph Biden and his wife Jill Biden attend the 'A Concert For Hope' event, hosted by Washington National Cathedral, to mark the tenth anniversary of the 9/11 terrorist attacks September 11, 2011 at the Kennedy Center in Washington, DC. The United States is commemorating the tenth anniversary of the terrorist attacks of September 11, 2001 which resulted in the deaths of nearly 3,000 people after two hijacked planes crashed into the World Trade Center, one into the Pentagon in Arlington, Virginia and one crash landed in Shanksville, Pennsylvania.