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.

To restore their legitimacy in the eyes of all citizens, police departments could begin by acknowledging their role in past injustices. In his response to our study, Edward Flynn, the police chief of Milwaukee, had the opportunity to do just that. Instead of addressing the implications of our study’s results, though, he dismissed them by claiming that our data were affected by technological quirks in the 911 system. But our study accounted for these considerations by showing that not all 911 calls went down after Mr. Jude’s beating made headlines, just calls reporting crime to the police.

What explains our finding is not some administrative glitch but the fact that police violence against an unarmed black man was registered in the collective memories of black Milwaukeeans as part of a larger pattern. Before Frank Jude, there was Justin Fields, an unarmed black man shot in the back by a Milwaukee police officer in 2003. Before Justin Fields there was Mario Mallett, a black man who, handcuffed and shackled, died in the back of a police wagon after a struggle with officers. Before Mario Mallett there was Thomas Jackson, a mentally ill man who suffocated after police officers placed their knees in his back while he was handcuffed. Before Thomas Jackson, there was James Philips III and Nicholas Elm Sr., who died in police custody; before them, there was Tandy O’Neal, shot in the back during a police raid; before him, there was Ernest Lacy, a black man falsely accused of rape, who died after officers used excessive force while arresting him. Some of us have forgotten these names; some of us cannot.