President Barack and Michelle Obama bow their heads during a memorial service for the victims of the fertilizer plant explosion last week, at Baylor University in Waco, Texas, April 25, 2013. [Photo/Agencies]

US first lady Michelle Obama wipes a tear during the playing of "Amazing grace" as she attends the a memorial ceremony for the victims of the fertilizer plant explosion in West, Texas, held at Baylor University in Waco, Texas, April 25, 2013. [Photo/Agencies]