In the six months after Mr. Jude’s story was published, homicides in Milwaukee jumped 32 percent. Our research suggests that this happened not because the police “got fetal” but because many members of the black community stopped calling 911, their trust in the justice system in tatters. Research shows that urban neighborhoods with higher levels of legal cynicism also have higher rates of violent crime: When citizens lose faith in the police, they are more apt to take the law into their own hands.

Our findings confirm what the people of Ferguson, Mo., Baltimore and other cities have been saying all along: that police violence rips apart the social contract between the criminal justice system and the citizenry, suppressing one of the most basic forms of civic engagement, calling 911 for help. The promotion of public safety requires both effective policing and an engaged community. We cannot have one without the other.

No act of police violence is an isolated incident and it should not be treated as such. Each new tragedy contributes to and reawakens the collective trauma of black communities, which have been subjected to state-sanctioned assaults — from slave whippings and lynching campaigns to Jim Crow enforcement and mass incarceration — for generations. If acts of excessive police force result in community-level consequences, then cities should implement community-level interventions in the aftermath of such acts.