THE last time Baltimore rioted in the way it did last night was in 1968, after the murder of Martin Luther King. In the neighbourhoods of West Baltimore, where the broken glass and burning cars are being cleared up this morning, the derelict houses and vacant lots are partly a legacy of that riot almost half a century ago. Like then, this latest bout of chaos began as an outpouring of anger, this time against the treatment of Freddie Gray, a 25-year-old who died in mysterious circumstances on April 19th, having apparently suffered injuries while being arrested.

Extreme lawlessness in an already troubled city Yet the difference between 1968 and today is that Baltimore is no longer a place where blacks are straightforwardly oppressed. Its population is 63% African American. Its mayor, Stephanie Rawlings-Blake, is a black Democrat who won 87% of the vote in 2011. Her police commissioner, Anthony Batts, is black, too, as are most of the city’s police. Baltimore, like Washington DC, Philadelphia and Detroit—and completely unlike suburbs such as Ferguson, Missouri—is a centre of black political control. So why is the city’s police department so troubled?

There are plenty of reasons. Institutions do not change easily, whoever is in charge. The struggle of blacks in America these days is rarely about the malign intentions of individual racists in power, but rather is more about structural problems such as concentrated poverty, broken families and terrible schools.

It does not help, either, that Baltimore is one of the most dangerous cities in America. Its murder rate in 2013 was 37 per 100,000—worse than South Africa’s. In one week of June of that year, the city saw ten murders and 28 shootings among a population of just 622,000. Baltimore is a city where young black men are occasionally killed by the police—and where most days a young black man is murdered by another young black man.

To say that is not to excuse Baltimore’s police department, which has a history of extraordinary violence. But it seems relevant in analysing the problem that many African Americans have with the police. Many young black men resent cops who endlessly search them; who stop their cars and fine them; who treat them like criminals, not fellow citizens. But if you visit a police community meeting in a black neighbourhood, as your correspondent did in the south-east of Washington, DC recently, you discover that the middle-aged, middle-class black women who attend have a different problem. They complain that the police are not doing enough to stop violent crime.

What police officers say about police violence Historically, the problem with policing for black Americans has not been its presence but its absence, argues Jill Leovy in “Ghettoside”. For much of the 20th century, police in America put a lot of effort into protecting white people and their property from black people, but often ignored black-on-black violence. This, Ms Leovy contends, is one of the reasons why black neighbourhoods tend to suffer so much higher violent-crime rates. When criminals are not punished by the law, they run wild. Each act of violence can spark a cycle of retribution. Scores are settled with fists, knives or bullets. "Snitching" comes to be seen as shameful. When the police do try to solve crimes, they find that no one will tell them anything useful. In Baltimore the murder rate has fallen by a fifth since its peak in the 1990s, but the clearance rate for murders is still well under 50%, compared with a national average of 65%. The Baltimore police department has too few officers—3,000 or so—to investigate more than 200 murders a year while also doing everything else that modern police departments have to do. And because they are overwhelmed, they struggle to gain the trust they need to get people to talk to them, and thereby to reduce the number of murders. In 2005 a white mayor, Martin O’Malley (who now seems likely to run for president), introduced “zero tolerance” policing, urging cops to stop and search young men acting suspiciously for guns or drugs. In that year, the city’s police made 100,000 arrests, among a population only six times that. Within a few years that policy was abandoned in favour of a more targeted approach—but only after huge damage had been done to relations between the police and black civilians. The only long-term way to reduce violence is to know more about who is perpetrating it. That means creating an environment where people have faith that the law will protect them—something that most Americans take for granted but residents of inner cities do not. The Boston Gun Project showed that by a mix of intelligence and aggressive targeting of people involved in shootings, the murder rate in black inner-city neighbourhoods can be cut substantially. In Britain, projects such as the Trident programme in London, in which specialised officers built up close links with the friends and relatives of suspected criminals, have had a similar effect in reducing black-on-black teenage knife and gun crime.

But the trouble with these long-run strategies is that they require time, money and luck to work. Trust cannot be built quickly. And police departments are seldom radical places: things are done the way they always have been. For a lot of politicians, flooding the streets with blue uniforms to collar criminals is easier—it reassures the public that something, anything, is being done.