general martin dempsey , chairman of the joint chiefs of staff , sent a letter saying he regretted that he ` added to the grief ' of debbie lee , whose son marc was killed in august 2006 .
the 28-year-old , the first navy seal to die in iraq , was fatally wounded while providing covering fire from a building in the heavily-contested city .
he was awarded the purple heart and silver star for his bravery .