KANDAHAR, AFGHANISTAN—Friends, family, and colleagues of 19-year-old U.S. Marine Alex Penzerton were saddened Wednesday upon learning he had been killed by a roadside bomb and was thus deprived of the life-changing opportunity a few years in the military might have afforded him. "Alex was a troubled kid who really could have benefitted from the kind of structured environment an organization like the Marines provides," said Penzerton's father, David, holding the flag the Corps had shipped home to him. "I'm sure he would have straightened himself out if he'd just had a few more months in the service and survived into his 20s." Also killed in the attack was 26-year-old Cpl. Damon Siggs, who sources said was in his fourth tour of duty and had really turned his life around with the discipline he learned as a Marine.