"Although inquest juries have delivered verdicts of unlawful killing in at least twelve cases, no one has been convicted for their part in these deaths over the two and a half decades," the report reads.
Compounding the problem, authors say, is a so-called joint enterprise law used by law enforcement officials as a "dragnet device" in convictions. Joint enterprise paves the way for murder convictions "even if the unlawful act occurs spontaneously and solely on the basis of an individual's presence at the scene" of the crime.
In contrast, pursuing legal action over the 509 deaths in custody is further complicated by self-defense, necessary action and legitimate purpose legal protections.
"As more deaths take place and no one is ever prosecuted, it inevitably sows seeds of incredulity, anger and despair," Harmit Athwal, the study's co-editor, said in a press statement.
According to a poll conducted by the United Kingdom's National Center for Social Research in 2013, up to one-third of Britons admitted to feelings of racial prejudice.