People pay tribute to Sergent Ron Helus, who was killed in confrontation with the shooter, at Los Robles Medical Center in Ventura County, California, the United States, on Nov. 8, 2018. A U.S. Marine veteran opened fire in a crowded bar popular with college students in the state of California, killing 12 people including a sheriff's deputy, police said on Thursday, in the latest mass shooting that shocked the country. (Xinhua/Qian Weizhong)