All of those. (By the way, I didn't even know about this sorry tale until I saw the article you shared on FB. Near enough **** all coverage of it here all about the Chilcot report.)
Not sure I can give you a satisfactory answer on a forum. Some causes are historic ie slavery, segregation. Some causes are economic such as poverty. Some causes are cultural prevalence of guns, lack of trust in the police, racism. Some causes are the way we hire cops, such as hiring ex-soldiers, hiring people with violent tendencies, hiring psychopaths as police officers (one of the highest jobs they get). Some causes are structural in the police departments, lack of community policing, poor training, lack of accountability. Some of it is the prevalence of camera phones (it isnt like this is a new problem you just see it more now). Some of it is the size of our population and the number of cops we have (new york city alone has more than 10,000 police officers). Its probably all of those and more, I have had cops pull guns on me twice. It isnt a rare thing for a cop to pull a gun and as such it isnt a rare thing for a cop to shoot someone. We have an estimated 700-1,000 people shot and killed by the police every year. This is at least the 114 shooting of an african-american so far this year. Its hard to know how many really as only a few police departments in the US report shootings to the federal government. I only share a few of these things a year on facebook so you can imagine how many of them we have that you dont see.
