Even before protesters burned Baltimore, before they filled the streets of New York and other cities, police departments across the nation had begun to retreat from the aggressive tactics of the 1990s that focused heavily on arresting petty offenders.

But a bitter legacy of anger lingers in West Baltimore and other urban neighborhoods. And the disturbances that have erupted after the death of Freddie Gray and other men stopped by police for minor violations are likely to accelerate the trend away from mass arrests and zero tolerance, policing experts said.

“There are cycles in policing, just as there are cycles in economics . . . [and] the tide is turning,” said Thomas Reppetto, a former Chicago police detective and the author of a two-volume history of policing in America. “We’re hearing a lot of the same things that we heard in the 1960s: The police have got to be less aggressive.”

New York City has already drastically reduced its controversial “stop and frisk” program, in which police questioned and patted down large numbers of pedestrians. The city is considering using warnings instead of arrests for low-level offenses such as public drinking or riding a bike on a sidewalk.

A presidential task force — appointed in response to the deaths of Michael Brown in Ferguson, Mo., and Eric Garner in Staten Island, N.Y. — issued a report in March urging less confrontational police practices and more respectful ties with residents.

In Washington, Police Chief Cathy L. Lanier said she gave up on “zero tolerance” because it ­“ruined” good relationships between police and residents of high-crime neighborhoods such as Barry Farm in Southeast Washington.

“What we forgot when we started that type of policing is that the neighborhoods that have the most homicides and shootings are also the neighborhoods that have the most victims and witnesses,” ­Lanier said March 25 at a town hall meeting on community-
police ­relations at American University.

“These are the people that can help you, that know what’s going on,” Lanier said. “We destroyed that relationship, and they didn’t trust us. So we’re going back and completely undoing that strategy.”

The protests last week in Baltimore highlighted the residue of rage left by “zero tolerance.” Martin O’Malley (D) became a champion of the strategy after his election as mayor in 1999. The result was a sharp spike in arrests that peaked in 2005, when Baltimore police made more than 100,000 arrests — one for every six city residents.

“The goal was to go out there and make as many low-level drug arrests as possible,” said former Baltimore police officer Neill Franklin, a frequent critic of O’Malley who was fired from the force during O’Malley’s tenure as mayor. Franklin now works for an organization that campaigns against the war on drugs. “Officers did whatever they had to do to lock up as many people as they could to satisfy police headquarters.”

After O’Malley left office in 2007, his successors pulled back. By 2013, the most recent year for which statistics are available, the number of arrests had fallen to just over 50,000. Police officials have also encouraged a softer community policing approach, including more foot patrols and stronger relationships between officers and the neighborhoods they serve.

However, many people who participated in the recent protests said Baltimore police continue to deploy overly aggressive tactics. Police chased and arrested Gray, for instance, because he ran from them. On Friday, State’s Attorney Marilyn J. Mosby called his arrest unjustified and filed criminal charges against the six officers involved.

Protesters march to City Hall in solidarity with Freddie Gray after it was announced that criminal charges would be brought against all six officers involved in the case. (Jabin Botsford/The Washington Post)

Harry Collic, 22, who demonstrated every day last week in West Baltimore, said he was frustrated that so many people in the neighborhood are routinely stopped or arrested for offenses such as loitering.

“We feel like targets,” said ­Collic, who works temporary jobs. “You can come home with your work uniform on, and they still check you for drugs.”

Another protester, Charmaine Slade, 24, who works for the city as a probation agent, also criticized police for what she called excessive arrests.

“I’ve got clients who are arrested 12 or 13 times a year. Their charges are dismissed, but they [were] still sitting in jails” without justification, she said.

The perception that police were overly aggressive in making arrests has fueled protests in other cities, including Ferguson and North Charleston, S.C., where police shot and killed Walter Scott last month after stopping him for a faulty taillight. In Staten Island, protests erupted after Garner died in July, when police used a chokehold to restrain him after arresting him for selling untaxed cigarettes.

In Ferguson, the aggressive tactics were aimed at raising revenue, according to federal investigators. But in many cities, including New York and Baltimore, they have been deployed as part of an intentional strategy to target petty criminals in the hope of preventing more serious crimes.

That strategy is known as the “broken windows” approach to policing, and it is based on the notion that a neighborhood that fails to fix the little things — e.g., broken windows — will quickly deteriorate. It was pioneered as a policing strategy in New York City, particularly under Mayor Rudy Giuliani in the mid-1990s.

Giuliani — and later O’Malley — credited the strategy with producing a sharp drop in homicides and other violent crimes. But these days, many criminologists question that claim.

Defenders of the strategy say the results are self-evident. As O’Malley tweeted Friday, FBI statistics show violent crime dropped by 41 percent while he was mayor, the largest reduction for any major U.S. city.

But skeptics note that violent crime has dropped sharply across the nation — and even around the globe — over the past two decades. The phenomenon is not fully ­understood and has been attributed to factors, including broad demographic trends, ­that have nothing to do with the police.

“Crime has gone down in every large urban area in the country, including places that haven’t practiced zero tolerance or ‘broken windows’ policing,” said Robert Gangi, director of the Police Reform Organizing Project in New York.

Because the rate of violent crime in the United States is at its lowest point in more than four decades, criminologists say it’s easier for authorities and the public to reassess the aggressive tactics adopted during a more violent era.

“Things that people might have been willing to tolerate, because crime rates were higher, are now much more visible,” said Jeremy Travis, president of the John Jay College of Criminal Justice. “These interactions between police and public are now being rethought.”

Los Angeles civil rights attorney Connie Rice, a member of the President’s Task Force on 21st Century Policing, agreed. Rice, who once sued police officers, now advises Los Angeles police on how to improve relations with minority communities.

“There’s nothing wrong with saying that in poor communities, it’s important to let the population know that we care about small crimes, because we don’t want big crimes,” Rice said. “The problem is when you execute it in such a ham-fisted way that you end up having a dragnet that ensnares most of the population — and humiliates most of the black or Latin community.”

Even those who see benefits from the aggressive tactics are starting to question their cost. Rob Weinhold spent years as a Baltimore police officer and agrees with O’Malley that the get-tough policies “yielded terrific results from a crime standpoint” in Baltimore.

But “when a department begins to arrest everyone for any infraction, the first thing that happens is your criminal justice system becomes overwhelmed,” Weinhold said. “And then it creates a lot of anger within the community.”

Peter Hermann contributed to this report.