Alex Tabarrok has an excellent book review of When Police Kill by Franklin Zimring (2017).
Tabarrok ends with this Zimring quote:
[Police killings]…are a serious problem we can fix. Clear administrative restrictions on when police can shoot can eliminate 50 to 80 percent of killings by police without causing substantial risk to the lives of police officers or major changes in how police do their jobs. A thousand killings a year are not the unavoidable result of community conditions or of the nature of policing in the United States.