A photograph of Shanann Watts and her daughters, Bella, 4, left, and Celeste, 3, is shown at a makeshift memorial in Frederick, Colo. (David Zalubowski/AP)

There are approximately 15,000 homicides in the United States each year. For the past week or so, only one of them has commanded the national news media’s attention.

The slaying of Shanann Watts, a pregnant Colorado woman, and her two young daughters has attracted airtime on ABC News, CBS News, CNN, Fox News and NBC News. The Washington Post, the New York Times and other newspapers have written stories about the grisly case; USA Today ran a live stream of a court appearance by the suspect, Watts’s husband, Christopher Watts.

The intense interest raises a question: What makes this crime different from the many terrible crimes that don’t rate even a mention on the local news, much less the national kind?

The Colorado story has some singularly lurid and media-centric elements — multiple deaths within a family, copious video footage of the victims and the suspect — but as with much of the coverage of crime in America, the story may reflect race, gender and class dynamics as much as any other detail.

The news media’s focus on the Watts slayings reinforces the conclusion of multiple studies of crime coverage not just in the United States but in other Western nations: that young, white, middle- and upper-middle-class female victims tend to attract disproportionate media attention compared with people from other backgrounds.

The most well-known and intensely covered “true crime” stories of the past 20 or so years have featured someone similar to Shanann Watts, who was 34 at the time of her death. Whether as victims or alleged perpetrators, each high-profile case has featured a white woman of a certain age — typically teens to late 30s — from reasonably privileged circumstances.

The victims list includes Laci Peterson, Chandra Levy, Lori Hacking, Natalee Holloway, Elizabeth Smart and Hannah Anderson, among many others. Women such as Amanda Knox, Jodi Arias and Casey Anthony have been alleged perpetrators, too.

Stories about young, white, female victims are “a natural trope” in American society, a variation of the classic “damsel in distress” tale that has been reinforced by movies, books and culture for centuries, said Zach Sommers, a sociologist at Northwestern University who specializes in criminal law.

Thus, viewers and readers relate to young white girls and women as “universal beings” in need of protection, he said. “The audience is more able to think, ‘That could be my daughter, my sister, my neighbor.’ There’s a built-in emotional attachment.”

That makes Shanann Watts — a young mother of two who was pregnant with her third child — the “ideal” victim for news media portrayals, said Michelle Jeanis, a criminologist at the University of Louisiana at Lafayette and the co-author of a 2016 study on missing-persons coverage. “When a victim is seen as more innocent, it invokes more fear in the public,” she said.

In a 2013 study of missing persons, Sommers compared national and local media coverage of missing people against the FBI’s missing-persons database; he found that African Americans received disproportionately less coverage than whites. Men also received disproportionately less coverage than women.

Network TV representatives declined to comment directly on their coverage decisions, describing them as internal matters. But privately, several made the same point, in effect justifying the coverage: The Watts story has attracted widespread interest among viewers.

“The viewer response has been overwhelming,” said one. “It’s not a typical run-of-the-mill crime story. It has a number of compelling elements for TV,” including a TV interview with Christopher Watts pleading for the safe return of his wife and daughters.

One network official compared the Watts story to that of Jeffrey MacDonald, the doctor and former Army officer who was convicted of killing his pregnant wife and two daughters in 1970 in a notorious case that became the basis for the book and miniseries “Fatal Vision.”

The Watts case, in fact, seemed to bump news coverage of the summer’s other “damsel in distress” story, the disappearance of Iowa college student Mollie Tibbitts, 20. Her remains were found Tuesday, just over a month after she was reported missing.

It would be easy to conclude that the news media is racially and economically biased in selecting which crimes to cover and which victims to portray, but the audience plays an important role, too, said Jeanis. The news media may create a skewed portrayal of victimhood, she said, but the audience rewards it and perpetuates it by responding to such portrayals time and again. “It’s hard to determine which is chicken and which is egg,” she said. “If there’s racial bias, who’s responsible for that?”

Similarly, the media’s focus on relatively prosperous victims may, in part, reflect something more than just a preference for the economically advantaged. People with a high degree of “social capital” — that is, family and social connections — are better able to spread the word to the news media and others about a crime than those who are economically disadvantaged and isolated, she said.

She contrasts the attention the Tibbitts case received this summer with that of Sebastian Husted, a 19-year-old Iowan missing since January. Tibbitts’s friends and family quickly distributed news of her disappearance this summer, drawing attention from local newspapers and TV stations, and eventually from national media outlets. Husted’s family, however, has lamented that they lacked the resources and community support to drum up similar attention for him.

In any case, the media attention on Christopher Watts is unlikely to subside even with his admission this week that he killed his wife. Watts will probably stand trial in the deaths of his daughters, which he has blamed on his wife. “My unscientific, educated guess is that if and when this goes to trial, there will be plenty of news coverage,” said Northwestern’s Sommer. “It will be very high profile.”