In Berkeley, California, a second night of protests against police killings of unarmed black men in Missouri and New York turned violent again Sunday as some demonstrators threw explosives at officers, assaulted each other and shut down a freeway, police said. The California Highway Patrol said some protesters made their way to a freeway in Oakland and blocked traffic. The CHP said some tried to light a patrol vehicle on fire and threw rocks, bottles and an explosive at officers, and that highway patrol officers responded with tear gas. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Tear gas helped the police drive protesters away from the highways. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Force was used against some protesters. Stephen Lam/Getty Demonstrators chanted about the apparent police immunity in New York and Ferguson. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty The protests have raged sporadically across the country since August. (REUTERS/Noah Berger) Noah Berger/Reuters Protests began peacefully but there were reports of arson and looting. (REUTERS/Stephen Lam) Stephen Lam/Reuters On a second night of unrest, police officers were equipped with riot gear. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images "Hands up. Don't shoot," has become a familiar refrain at protests across the country. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Some wore masks to protect against the effects of tear gas. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Four police officers were injured. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Six protesters were arrested. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Police forced demonstrators off the public highways. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Police fired tear gas. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images Protests spread from the university campus out into the city. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images There were no serious injuries reported. (Photo by Stephen Lam/Getty Images) Stephen Lam/Getty Images