Thousands Mourn in NY, DC, Penn.

President Obama visited the Pentagon to mark the anniversary of 9/11 Tuesday, saying, "This is never an easy day." Thousands gathered to mourn in New York, Washington, D.C., and Pennsylvania. Meanwhile, construction will resume at the National September 11 Memorial & Museum after the museum and the Port Authority came to an agreement Monday. All work at the memorial was halted last year over disagreements about funding, financing, and oversight. The federal government also announced it will add cancer to the list of illnesses linked to 9/11—making many former Ground Zero workers eligible for financial compensation.