A MARINE who helped in the rescue of US Army Private Jessica Lynch in Iraq was shot dead at a family barbecue in California, just 12 days before he was to be discharged.Lance Corporal Sok Khak Ung, 22, and a family friend, Vouthy Tho, 21, were killed on Monday in a garage at a Long Beach home by a gunman who fired six to eight shots before fleeing, police said.Yesterday, Los Angeles County Supervisor Don Knabe offered a $US10,000 ($14,000) reward for information on the killings."I am outraged that someone would so cowardly gun down this brave soldier," Knabe said....