In the basement of Charles Street AME, a church in Roxbury, a historically black neighbourhood in Boston, Haseeb Hosein, the captain of the local police district, delivers the good news.

"We've had no homicides in B2, year to date," he says. "Keep on praying," he says, to a chorus of "Amens".

"I can tell you, the district is going really well when we're focusing on barbershop music, when we're focusing on cars blasting music," he says. "Music is my biggest community concern and I am a happy camper."

It is not just B2. Across the whole city of Boston, by the beginning of this month there had been just 13 homicides this year.

That is a 50% reduction on the same point last year—which was already a record low.

This year, Beantown is on track to become the safest big city in America. Nationwide figures do not yet exist.

But according to AH Datalytics, which collects real-time crime data from 277 American cities, the number of murdersrecorded so far this year is down by 18% on the same period last year.

Some very violent cities, such as Philadelphia and Baltimore, have experienced improvements almost as big, in proportional terms, as Boston.

In Philadelphia there have been 111 fewer homicides this year than last.

Yet Boston is worth looking at, precisely because it shows how safe American cities could be, and what it would take to achieve that.

Even with the improvement, America remains a stunningly violent country. The national homicide rate is 14 times higher than it is in Italy.

Some of this is the inevitable result of guns being more freely available than elsewhere.

But much of what makes America's overall figures so big is the terrifyingly high level of murder among young black and Latino men.

Nationwide, a black teenage boy has a roughly one in 100 chance of being shot to death before he reaches the age of 30. Boston shows it is not inevitable.

Some suggest that Boston is safe because it is rich. The median household income is $86,000, compared with a national average of $75,000.

Thanks to the tech and finance industries, once-rough neighbourhoods like South Boston are now among the most expensive places to live anywhere in America.

Perhaps the criminals have been gentrified out? Another popular claim is that there are still shootings—it is just that more people survive because of advancing medical care.

"What you hear is, 'It's all, we're gentrifying, or Boston has the best trauma centres'," says Christopher Winship, a sociologist at Harvard University. "My argument is, that's not adequate." The data back Professor Winship up.

According to the Census Bureau, despite gentrification, Boston's black population has not shrunk in recent decades: black Bostonians continue to make up a fifth of the city's population, roughly the same share as in 1990.

As for wealth, whereas median incomes have grown, the poverty rate, at around 17%, is almost exactly the same as in Chicago.

If wealth alone could explain the fall in the murder rate, Washington, DC, a city even more gentrified, with a similar-size population, would be as safe as Boston.

Instead, in 2023 the capital suffered seven times as many murders.

As Reverend Eugene Rivers, an anti-violence activist in Boston, puts it: "What does white folks getting richer do if all of the murders are committed by poor blacks?"

So what does explain the improvement? Across America, high murder rates among young black men are the result of a lack of trust.

In segregated neighbourhoods people are reluctant to call the police because they do not expect them to take their complaints seriously.

Young men join gangs to get protection against being robbed or otherwise victimised. Extreme violence is a way of signalling that you should not be messed with.

In Boston, when teenagers with guns are arguing, Boston's police usually know how to stop it. This trust was built over decades.

In 1998 Reverend Rivers was among those who started the weekly get-togethers between police and community groups, known as the "Baker House" meetings.