In Chicago, 16-year-old Darryl Green was killed, relatives reported, because he refused to join a gang. Unlike most tragedies — which remain local news — this one caught the attention of conservative activist Ben Shapiro, who tweeted and publicized Green’s murder. But this wasn’t a call for help and assistance for Green’s family. Rather, it was his response to wide outrage over the acquittal of George Zimmerman in the killing of Trayvon Martin.

Shapiro, echoing many other conservatives, is angry over the perceived politicization of the Zimmerman trial, and believes that activists have ”injected” race into the discussion, as if there’s nothing racial already within the criminal-justice system. He complains that media attention had everything to do with Zimmerman’s race. If he were black, the argument goes, no one would care.

And so, Shapiro found the sad story of Darryl Green, and promoted it as an example of the “black-on-black” crime that, he believes, goes ignored. Or, as he tweets, “49 percent of murder victims are black men. 93 percent of those are killed by other blacks. Media don’t care. Obama doesn’t care. #JusticeForDarryl.”

The idea that “black-on-black” crime is the real story in Martin’s killing isn’t a novel one. Zimmerman defense attorney Mark O’Mara has said that his client “never would have been charged with a crime” if he were black.

But there’s a huge problem with this attempt to shift the conversation: There’s no such thing as “black-on-black” crime. Yes, from 1976 to 2005, 94 percent of black victims were killed by black offenders, but that racial exclusivity was also true for white victims of violent crime — 86 percent were killed by white offenders. Indeed, for the large majority of crimes, you’ll find that victims and offenders share a racial identity, or have some prior relationship to each other.

What Shapiro and others miss about crime, in general, is that it’s driven by opportunism and proximity. If African-Americans are more likely to be robbed, or injured, or killed by other African-Americans, it’s because they tend to live in the same neighborhoods as each other. And of course, the reverse holds — whites are much more likely to live near other whites.

Nor are African-Americans especially criminal. If they were, you would still see high rates of crime among blacks, even as the nation sees a historic decline in criminal offenses. Instead, crime rates among African-Americans, and black youth in particular, have taken a sharp drop. Overall, figures from a variety of institutions — including the FBI and the Bureau of Justice Statistics — show that among black youth, rates of robbery and serious property offenses are at their lowest rates in 40 years, as are rates of violent crime and victimization.

“Black-on-black crime” has been part of the American lexicon for decades, but as a specific phenomenon, it’s no more real than “white-on-white crime.” Unlike the latter, however, the idea of “black-on-black crime” taps into specific fears around black masculinity and black criminality — the same fears that, in Florida, led George Zimmerman to focus his attention on Trayvon Martin, and in New York, continue to justify Michael Bloomberg’s campaign of police harassment against young black men in New York City.