The question of why police can kill civilians and get away with it isn’t new and isn’t going away. Whether it was a grand jury’s decision in late 2014 not to press charges against the cop who killed Michael Brown in Ferguson, Missouri or a prosecutor’s decision a year later on the cops who killed 12-year-old Tamir Rice in Cleveland, or June’s acquittal in Baltimore of the latest officer facing charges for killing Freddie Gray in April 2015, or a video released this week by police in Fresno, Calif., where officers killed a mentally unstable Dylan Noble on June 25, the same questions, legal assessments and lack of accountability seem to recur—even as the victims’ circumstances differ.

Noble was unarmed, but kept walking toward officers while hiding one hand even as the cops warned him and threatened to shoot. The police killings this month of Alton Sterling in Baton Rouge, Louisiana and Philando Castile near Minneapolis, Minnesota, followed a similar script, in which the officers involved claimed they felt threatened. In all these cases, a complex and volatile mix of factors involving race, police fear, state-sanctioned power and weaponry, questionable training and unaccountable systems interacted.

In 2014, there were 444 “justifiable” homicides by law enforcement, according to FBI statistics. In 2013, there were 461 justifiable homicides, the FBI said. Academic criminologists say that number is closer to 1,000 annually, because not all local department report to the FBI. Between 2005 and 2015, 47 officers have been charged with murder or manslaughter, and 13 have been convicted of murder or manslaughter from fatal on-duty shootings.

There are many factors surrounding police killings and what’s almost always exoneration under America’s criminal justice system. Some are well-known and others less so, but all point to a police culture and criminal justice system that enables cops to target perceived threats, encourages the use of force and is reluctant to second-guess law enforcement when tragedy ensues.