Ghettoside: A True Story of Murder in America. By Jill Leovy. Spiegel & Grau; 384 pages; $28. Bodley Head; £16.99.

VIOLENT crime in America has dropped dramatically in the past 20 years. In both New York and Los Angeles, the number of murders fell from about 2,000 a year in the early 1990s to a quarter of that number today. But though far fewer are being killed, black men are still dying at alarming rates in the toughest urban pockets. One such is a part of Los Angeles known as Watts, the subject of a harrowing investigation by Jill Leovy, a veteran police reporter for the Los Angeles Times.

In 2007, frustrated that so little attention was being paid to these street murders, Ms Leovy started a blog for her paper called “Homicide Report”, describing every single murder in the city. Now, after a decade shadowing an LAPD homicide squad, she has gathered all she learned into a book to stress that this epidemic of murder is still raging. At a time when the Twitter hashtag #BlackLivesMatter is a rallying cry against police killings of black men, her aim in “Ghettoside” is to show that black lives in the inner city matter too—and must be made to matter more.

Ms Leovy powerfully portrays the cycle of violence in Watts through the true story of a single murder, told with the chilling detail and gripping pace of a prime-time drama. Bryant Tennelle is the 18-year-old black son of an LAPD detective, a good boy gunned down by mistake; John Skaggs, a blond surfer turned homicide detective, doggedly investigates. As she chronicles the case, Ms Leovy weaves in other heartbreaking stories, taking the reader into police interrogations, the homes of grieving mothers, and hospitals where parents plead for the lives of their dying sons. A portrait emerges of a traumatised community cut off from the world, where thugs kill with impunity and residents are too terrified of reprisal to provide information to the cops.

The strength of “Ghettoside” lies in its blunt reminder of an ugly fact: murder victims in America are disproportionately black men. They represent 6% of America’s population, but account for 40% of its murder victims, according to one study cited. For all the gains, Ms Leovy notes, two damning statistics have not budged for 30 years: the murder rate for black people remains five to seven times that of whites, and less than half of those doing the killing are caught and punished.

The violence is usually attributed to a hopeless cocktail of drugs, gangs and guns. But in Watts this is false, Ms Leovy reports. In recent years the drug trade has accounted for only 5% of local killings; black murder rates have held steady no matter what the motive. A root cause of the violence, she says, is the state’s “inability to catch and punish even a bare majority of murderers”. Indifference to black deaths has resulted in a parallel culture of rough justice that operates independently of the legal system, like other “vengeance cultures” from Northern Ireland to South Africa, Ms Leovy argues. Witnesses will not talk, so bringing suspects to justice is hard.

Detectives like Mr Skaggs, with his near-flawless record of solving cases, show that things can be different. The conviction of Tennelle’s murderers is an example of how cops can catch the bad guys and bring relief to the community, if they throw enough manpower at the problem. (Never mind that not all victims are the sons of cops, a fact the author does not really acknowledge.) Herein lies the book’s main weakness. Ms Leovy is so close to the homicide squad that she rarely looks beyond it. Little is heard from residents about why they distrust police, for example. Nor can readers assess complaints that “no one cares” about these black victims without understanding how the LAPD spends its vast budget. This is a compelling report from the trenches, but more remains to be written, and done.