The riots that devastated urban America during the 1960s were often ignited by acts of police brutality that inflamed poor African-American communities where the police were seen not as protectors but as an occupying force. These same tensions resurfaced last year in the suburban St. Louis community of Ferguson, Mo., where riots broke out after a white police officer shot and killed Michael Brown, a black teenager. They have now erupted on a larger stage, in Baltimore, after the death of Freddie Gray, a young black man who suffered a catastrophic injury while in police custody.

President Obama has condemned as inexcusable the looting and arson that spread across the face of the city after of Mr. Gray’s funeral. But he also implied that the Baltimore Police Department had “to do some soul-searching.” Indeed it does: A well-documented history of extreme brutality and misconduct set the stage for just this kind of unrest.

Proof can be found in a meticulously reported investigation by The Baltimore Sun of lawsuits and settlements that had been generated by police-brutality claims. “Over the past four years,” the investigation noted, “more than 100 people have won court judgments or settlements related to allegations of brutality and civil rights violations.” The victims included a 15-year-old boy riding a dirt bike, a 26-year-old pregnant woman who had witnessed a beating, a 50-year-old woman selling church raffle tickets, a 65-year-old church deacon and an 87-year-old grandmother aiding her wounded grandson.

The report, published last fall, detailed what it called “a frightful human toll” inflicted by the police: broken bones, head trauma, organ failure, and even death, occurring during questionable arrests. It found that judges and prosecutors routinely dismissed charges against the victims and that city policies helped to hide the extent of the human damage. Settlements prohibited the victims from making public statements. The Sun estimated that the cash-strapped city had spent $5.7 million on settlements and $5.8 million on legal fees since January 2011.

Baltimore residents were familiar with these and other stories of police abuse when Mr. Gray’s case fell into the public spotlight earlier this month. The police chased and apprehended him on April 12, allegedly because he had “made eye contact” with a lieutenant and then ran away. Cellphone videos of his arrest showed him being dragged into a police van, appearing limp and screaming in pain. The police have acknowledged that they delayed in calling for medical help. When he arrived at the police station, medics rushed him to the hospital, where he slipped into a coma and died a week later.

His family has said that 80 percent of his spinal cord was severed and that his larynx had been crushed. This account is at odds with a police report claiming that “the defendant was arrested without force or incident.”

The Baltimore Police Department has a particularly egregious history and has entered into a voluntary reform agreement with the Justice Department. But there is no reason to believe that it is unique in terms of its toxic relations with the people it is meant to protect.

Indeed, over the last five years, the Justice Department has opened 21 investigations into local police departments around the country and is enforcing reform agreements with 15 departments, some investigated by previous administrations.

Mr. Obama was right on the mark when he observed on Tuesday that tensions with law enforcement had simmered in African-American communities for decades and now seemed to be bursting into view once a week.

“This has been a slow-rolling crisis,” he said. “This has been going on for a long time. This is not new, and we shouldn’t pretend that it’s new.”

He also said that addressing the problem would require not only new police tactics but new policies aimed at helping communities where jobs have disappeared, improving education and helping ex-offenders find jobs. The big mistake, he said, is that we tend to focus on these communities only when buildings are burning down.