“He knew what he was doing.” So said one eyewitness about 28-year-old Ian Long, the former Marine who gunned down 12 people Wednesday night at the Borderline Bar and Grill in Thousand Oaks. While mourners staged a vigil Thursday, many survivors’ thoughts turned to last year’s mass shooting at a Las Vegas country music festival. Some who survived that attack were at Borderline, where at least one was killed. “I learned from Vegas not to think twice, but to just get out,” one survivor said. Police have not yet identified Long’s motive.