In her timely new book, Jill Leovy examines one of the most disturbing facts about life in America: that African-American males are, as she puts it, “just 6 percent of the country’s population but nearly 40 percent of those murdered.” Leovy describes neighborhoods steeped in pain: A mother, dressed in a baggy T‑shirt adorned with her murdered son’s picture, spends all day indoors, too terrified to step outside; the brother of a homicide victim purposely meanders through violent streets in the hopes that he too will meet the same fate; grieving parents all wear the same haunted expression, the empty stare that one police chaplain calls “homicide eyes.” Leovy’s focus is South Los Angeles, though similar stories abound in many of the nation’s poorest communities.

This is a world that most journalists never cover, and most of America never sees. Leovy, a reporter for The Los Angeles Times, argues that as a nation we have grown far too accepting of our high rate of homicide — all the yellow crime-scene tape and sidewalk candle memorials — in large part because the media has paid too little attention. In response, she started a blog at her newspaper in late 2006 called The Homicide Report, in which she attempted to cover every murder in Los Angeles County in a single year. It was a radical idea — at the time, her paper reported on only about 10 percent of homicides — and also a near-impossible task: In a 2008 article, Leovy acknowledged that the report “has merely skimmed a problem whose true depths couldn’t be conveyed.”

In “Ghettoside,” she tackles this “plague of murders,” as she calls it, with a book-length narrative that enables her to write about it with all the context and complexity it deserves. Her protagonist is John Skaggs, a Los Angeles Police Department homicide detective, whom she portrays as both compassionate and relentless: He gives his personal cellphone number to the mothers of men who’ve been murdered, and he treats every homicide case “like the hottest celebrity crime in town,” Leovy writes, no matter how poor and unknown the victim was. Despite his white skin, Skaggs manages to win the trust of the community.

The narrative arc of “Ghettoside” traces one of Skaggs’s homicide cases: the murder of Bryant Tennelle. (The book’s title comes from a Watts gang member’s shorthand for his neighborhood and others like it — a term local detectives adopt.) One evening in 2007, Bryant walks outside with a friend not far from his home, carrying a root beer and pushing his bicycle, when a stranger jumps out of a car, shoots him and escapes. Like so many murder victims, Bryant is young (just 18 years old) and nonwhite. But as it happens, he is also the son of Wallace Tennelle, a highly respected African-American detective with the Los Angeles police. Tennelle is the first detective to arrive at the crime scene, only to find his son splayed on the grass, his brain matter everywhere.