J. Richard Cohen is a civil rights lawyer and president of the Southern Poverty Law Center.

White ribbons commemorating shooting victims are placed on a railing outside Emanuel AME Church in Charleston, S.C. (Mladen Antonov/AFP/Getty Images)

A white man and apartheid admirer walked into a black church Wednesday night and killed nine people. He reportedly said he had “to do it” because black people “rape our women” and are “taking over our country.”

The violent attack against Emanuel AME Church in Charleston, S.C., is an obvious hate crime, one that will, presumably, get reported to the FBI.

The vast majority of hate crimes, though, don’t. Our national system of collecting and reporting this data is disturbingly inadequate, overlooking most hate crimes each year. This underreporting is a problem because, lacking an understanding of the scope of the problem, law enforcement agencies and communities are less likely to devote the sustained resources and training needed to prevent and solve hate crimes.

According to the FBI’s most recent annual hate crime report, which is based on voluntary reporting by law enforcement agencies across the country, there were 5,928 hate crimes in 2013. In South Carolina, the FBI report says, there were 51. Those numbers vastly underestimate the problem, according to the Department of Justice’s Bureau of Statistics. A comprehensive analysis in 2013 showed that about 260,000 people are victimized each year by hate crime. The statistics bureau’s estimate is based on the National Crime Victimization Survey, the nation’s primary source of information on criminal victimization.

Why this mismatch?

First, many law enforcement agencies simply refuse to cooperate in the collection of data. Mississippi, for example, reported just four hate crimes in 2013; Alabama reported six.

Second, about a quarter of hate crime victims never report attacks against them, according to the Bureau of Statistics. Undocumented Latino immigrants, for example, may be reluctant to call the police because they fear being deported. Members of the LGBT community may remain silent because they want to keep their sexual orientation private.

Another reason that victims may decide not to report hate violence: A sense that nothing will be done. A mere 4 percent of cases end with an arrest.

This is particularly troubling because we’re in the midst of a strong – and often violent – backlash to the growing diversity and tolerance in our country. Hate groups that vilify minority groups, for example, have risen dramatically in the past 15 years – from 457 in 1999 to a peak of 1,018 in 2011. Though the numbers have declined since 2011, to 784 last year, they remain at historically high levels.

In addition to these groups, there has been a disturbing pattern of recent hate violence and domestic terrorism. Earlier this year, the Southern Poverty Law Center released a study of domestic terrorism incidents, including successful attacks and plots foiled by law enforcement, over the past six years. We found that such an incident occurred every 34 days – far more often than most Americans imagine.

The vast majority of these plots, more than 90 percent, were hatched not by organized hate or terrorist groups but rather by “lone wolves” or “leaderless resistance” groups of no more than two people.

Many of these people spent time reading extremist propaganda and interacting with others on white supremacist or radical, antigovernment Web sites. In this way, they can remain anonymous but still “belong” to an extremist movement even if they aren’t card-carrying members of a group. It would not be surprising if we discover in the coming days that the suspect in Wednesday’s shooting, Dylann Roof, fits this profile.

The tragedy in Charleston exposes the racial fault lines in our society and the backlash against our growing diversity. President Obama ran on the promise of “change.” But, for many, he represents the kind of change that they fear. We should, as a nation, make the fight against such domestic hate crime a top priority, as we do fighting terrorism. Part of that is understanding and accurately quantifying the scale of the problem so we can mobilize the country to do something about it.