Rebekah Gregory, who lost part of her left leg in the 2013 Boston Marathon bombing, on Wednesday condemned accused attacker Dzhokhar Tsarnaev in a letter posted to her Facebook page. "You are a coward," she wrote. "A little boy who wouldn't even look me in the eyes to see that. Because you can't handle the fact that what you tried to destroy, you only made stronger." The trial of Tsarnaev, who faces 30 charges and a potential death sentence, began Wednesday with the defense admitting Tsarnaev carried out the attack.