CHARRED beams are all that remain of the top floor of one house. Nearby, a group of young men lounge on the wooden stoop of another once-handsome looking home, its windows boarded up. Many lots, behind chain-link fences, are abandoned. The morning sun dazzles: in the shade of large trees two sex-workers wait for custom. Otherwise the streets appear mostly deserted.

Drive around the downtrodden northern suburbs of St Louis, both in and beyond its city limits, and signs of economic decline and ongoing racial segregation are obvious. Prospects for its predominantly African-American residents look grim. Gangs are not especially a problem, but drug trading and gun violence are. Over two days alone, last weekend, six people were shot dead in St Louis. Police add that non-fatal shootings, “almost homicides”, get less attention but are also common, time-consuming and almost as distressing.

Statistics just released by the FBI show the national rate of violent crime fell by 0.9% last year, and the murder rate crept down too, by 1.4%. That modest improvement confirms a return—after a two-year upturn—to a two-decade trend of America getting slightly less violent. More striking is a recent analysis by the Brennan Centre for Justice, a think-tank, of 29 of the country’s biggest cities. Based on reported crime so far, it expects the murder rate in those areas to fall by 7.6% in 2018, led by big improvements in Baltimore, Chicago and San Francisco. Violence is typically worst in warmer months, so the forecast looks robust.

Such trends should be cheered, but offer little for St Louis, a city whose core contains 300,000 and which suffers from a persistently awful rate of violence. Last year it saw 205 homicides, giving St Louis the highest murder rate of any big city in America. (This year has seen some improvement.) Almost all of the city’s homicides take place in just a few neighbourhoods. The police plot a heat map of crimes in St Louis: clusters of glowing red dots show that murders typically occur close to each other, in the same distressed streets in the north.

That suggests an opportunity. Police should be able to attack a problem that is densely concentrated. A failure to do so, at first glance, suggests wilful neglect. “We do have a homicide rate we’d love to see smaller”, says Major Mary Warnecke, Commander of Investigative Services, which includes the homicide division for the metropolitan area. Then she rattles off reasons—lack of staff, long-running social and economic hardships, use of drugs and overly lax gun laws, criminals who skip over the Mississippi to nearby Illinois—that make improvements intensely difficult.

Her detectives clear only a dismal 52% of their murder cases, a slight gain on the past few years, she says. They rely heavily on co-operation of witnesses, who may not be forthcoming. Couldn’t police cultivate better ties with residents? They try, but lack time, she says. By one estimate, a detective succeeds in clearing cases when given five or fewer to handle per year. Ms Warnecke says her overworked 33 homicide detectives officially have 4.8 cases each, but low clearances mean cases, like bodies, pile up. The stats don’t capture the true picture: “in reality they each handle more like 11 or 12 cases.”

In theory technology can help. Three years ago the headquarters got a “real time crime centre”, an Orwellian collection of screens to relay images from cameras all over the city, letting police monitor for trouble. Pictures are matched with reports from Shotspotter—lots of microphones in public places that record sounds of gunshots. These are instantly analysed, letting police know precisely where and what type of weapons are in use. Police also want a drone for better aerial footage, though local regulations forbid it.

Gizmos, however, have limited impact. The cameras, many of which are privately owned, are mostly placed in commercial or prosperous areas, such as downtown, or in whiter parts of the city. The technology thus mostly preserves security in what are already relatively safe places. In the declining northern areas, much remains hollowed out, abandoned and forgotten.