U.S. Senate votes to open debate on gun control measures

Grave markers are erected in a mock cemetery to honor the victims of gun violence during a 24-hour vigil on the National Mall in Washington D.C., capital of the United States, April 11, 2013. The U.S. Senate on Thursday voted to open debate on gun control measures advocated by President Barack Obama and mostly Democratic lawmakers, clearing the first hurdle for relevant legislation. (Xinhua/Wang Yiou)