Police are rarely charged with homicide when it occurs in the line of duty. Philip Stinson of Bowling Green State University found only 31 non-federal police officers who were on duty were charged with murder or non-negligent homicide committed with a firearm from 2005 to 2011. That comes out to just about four a year. According to the FBI, police committed 2,706 justifiable homicides during that same period, or about 385 a year. "It is really hard to convict a police officer. They get a super presumption of innocence," says former federal prosecutor Laurie Levenson. Meanwhile, a police officer in Ferguson, Missouri pointed a rifle at protesters Tuesday night and told them "I'll fucking kill you."