When a white person kills a black man in America, the killer often faces no legal consequences.

In one in six of these killings, there is no criminal sanction, according to a new Marshall Project examination of 400,000 homicides committed by civilians between 1980 and 2014. That rate is far higher than the one for homicides involving other combinations of races.

When one person killed another 2 out of every 100 were found justified When a white person killed a black man 17 out of 100 were found justified 8 times as often

In almost 17 percent of cases when a black man was killed by a non-Hispanic white civilian over the last three decades, the killing was categorized as justifiable, which is the term used when a police officer or a civilian kills someone committing a crime or in self-defense. Overall, the police classify fewer than 2 percent of homicides committed by civilians as justifiable.

The disparity persists across different cities, different ages, different weapons and different relationships between killer and victim.

To understand the gaps, The Marshall Project obtained dozens of data sets from the Federal Bureau of Investigation and examined various combinations of killer and victim. Two types of “justifiable homicide” are noted: “felon killed by private citizen” or “felon killed by police officer.” (In a bit of circular logic, the person killed is presumptively classified as a felon, since the homicide could be justified only if a life was threatened, which is a crime.)

The data were processed to standardize key variables and exclude more than 200,000 cases that lacked essential information or were homicides committed by police. The resulting data detail the circumstances of each death; any weapons used; information on the killer’s and victim’s race, age, ethnicity and sex; and how police investigators classify each type of killing (“brawl due to the influence of alcohol”, “sniper attack” or “lover’s triangle”, for example).

Little large-scale research has examined the role of race in “justifiable” homicides that do not involve police. The data examined by The Marshall Project are more comprehensive and cover a longer time period than other research into the question, much of which has focused on controversial “Stand Your Ground” laws.

In the United States, the law of self-defense allows civilians to use deadly force in cases where they have a reasonable belief force is necessary to defend themselves or others. How that is construed varies from state to state, but the question often depends on what the killer believed when pulling the trigger.

“If there are factors—even if they're stereotypes—that lead the defender to believe he's in danger, that factors in, whether it’s a righteous cause or not,” said Mitch Vilos, a Utah defense lawyer, gun rights advocate and the author of “Self-Defense Laws of All 50 States.”

Self-defense decisions by regular people, much like those involving the police, are made quickly and with imperfect information. As a result, a homicide can be ruled self-defense when the killer faced no actual threat but had a reasonable belief he or she did.

That is where irrational fear can come into play. Police, prosecutors and juries may be apt to give killers the benefit of the doubt in situations when they were faced with someone who seemed “dangerous.”

“Tell me that it doesn’t factor in if the person is black when they're approaching the suspect,” Vilos said. “It contributes to the decision to pull the trigger because of the fear associated with the stereotype.”

“Right or wrong, that’s what’s happening, in my opinion,” he said.

The vast majority of killings of whites are committed by other whites, contrary to some folk wisdom, and the overwhelming majority of killings of blacks is by other blacks.

But killings of black males by white people are labeled justifiable more than eight times as often as others. This racial disparity has persisted for decades and is hard to explain based solely on the circumstances reported by the police data.

In comparison, when Hispanics killed black men, about 5.5 percent of cases were called justifiable. When whites killed Hispanics, it was 3.1 percent. When blacks killed whites, the figure was just 0.8 percent. When black males were killed by other blacks, the figure was about 2 percent, the same as the overall rate.

Although the data examined ends shortly after the fatal police shooting of Michael Brown in Ferguson, Mo., in 2014, reform efforts since then have primarily focused on police shootings. That leaves these cases largely forgotten.

Homicides have trended down since the 1980s. The percent of homicides ruled justified has remained fairly stable, ranging between about 1.5 and 3 percent annually. When a white person killed a black man the rate was consistently higher. One in six such cases was determined to be justified.

Note: Three-year rolling averages are shown; not all jurisdictions participate every year.

It is impossible to say to what extent the disparities—no matter how great—are due to racial prejudice by police, prosecutors or juries. One possible explanation for the differing rates could lie in the different circumstances of the killings, including where they happened.

“If, for instance, white-on-black homicides were mainly defensive shootings in a residence or business, and black-on-white shootings mainly occurred during the commission of a street crime, then the [racial] disparity would be warranted,” wrote researcher John Roman in a 2013 Urban Institute study of justifiable homicides.

Although the F.B.I.’s Supplementary Homicide Report tracks more than 100 details about each killing, the location of the death is not recorded. In addition, some police agencies, indeed some states entirely, choose not to share some or all information on killings.

Still, the disparities in how police classify these cases remain across widely different circumstances and causes of death. Whether the killer and victim were married, lovers, neighbors or complete strangers, whether they were shot, stabbed or beaten, the trend holds. The killings of black men by whites were two to 10 times as likely to be called justifiable.

Even after adjusting for the ages of the killer and victim, their relationship and the weapon used, the likelihood of a white-on-black-male case being called justifiable was still 4.7 times higher than in other cases.

When a stranger was

killed 5% were found justified 34% when a white person killed a black man 7 times as often When a romantic partner

was killed 1% were found justified 6% when a white person killed a black man 6 times as often When a friend or

acquaintance was killed 1% were found justified 3% when a white person killed a black man 3 times as often When the relationship

was unknown 1% were found justified 8% when a white person killed a black man 8 times as often

When a handgun was

used 3% were found justified 26% when a white person killed a black man 9 times as often When another type of

firearm was used 2% were found justified 17% when a white person killed a black man 8 times as often When a knife or other

object was used 1% were found justified 4% when a white person killed a black man 4 times as often When the killer was

unarmed 1% were found justified 3% when a white person killed a black man 3 times as often

Beyond the police consideration of each case, there are three additional stages at which a killer can establish self-defense: a prosecutor can decide not to pursue charges, a grand jury can decline to indict the killer and a jury can find a killer not guilty.

There is no national standard for how a prosecutor’s office decides whether or not to prosecute a case.

In Miami, for instance, an individual assistant state attorney can determine whether to take a homicide case to a grand jury or, with the approval of a supervisor, to decline to prosecute. In Phoenix, however, each case goes through a detailed review by a panel of prosecuting attorneys before a decision is made, according to officials there.

The F.B.I. data may not reflect those determinations: prosecutors are not generally required to collect and report their data. Despite these flaws, the data are the closest thing available to a comprehensive, nationwide accounting of homicides.

Despite local customs and policies for how prosecutors approach self-defense cases, in the F.B.I.’s data almost every law enforcement agency, from Oakland, Calif., to Philadelphia, showed disparities in how they categorized killings as justified. The phenomenon is not peculiar to any state or region.

When Houston police investigated homicides 3% were found justified 37% when a white person killed a black man 12 times as often Oakland, Calif., police 5% were found justified 32% when a white person killed a black man 6 times as often Phoenix police 4% were found justified 31% when a white person killed a black man 8 times as often Harris County, Texas, Sheriff 4% were found justified 28% when a white person killed a black man 7 times as often

Los Angeles police 2% were found justified 25% when a white person killed a black man 12 times as often Sacramento, Calif., police 4% were found justified 26% when a white person killed a black man 6 times as often Oklahoma City police 3% were found justified 23% when a white person killed a black man 8 times as often Philadelphia police 3% were found justified 23% when a white person killed a black man 8 times as often

Long Beach, Calif., police 4% were found justified 24% when a white person killed a black man 6 times as often San Diego police 4% were found justified 24% when a white person killed a black man 6 times as often Dallas police 2% were found justified 15% when a white person killed a black man 8 times as often Sacramento County, Calif., Sheriff 3% were found justified 14% when a white person killed a black man 5 times as often

Fort Worth, Texas, police 1% were found justified 9% when a white person killed a black man 9 times as often Portland, Ore., police 4% were found justified 10% when a white person killed a black man 2 times as often San Francisco police 2% were found justified 6% when a white person killed a black man 3 times as often New York police 1% were found justified 4% when a white person killed a black man 4 times as often

Note: New York State did not report data after 2006.

In all cases and at each stage, the system depends on the reports and decisions of police investigators, which provide the record upon which conclusions are drawn. Melba Pearson, a former prosecutor, said that in her experience, personal preconceptions affect how those cases are policed and whether they are prosecuted.

“The reality is every human being comes to the table with biases,” said Pearson, former president of the National Association of Black Prosecutors. “That’s human nature.”

Pearson called that a larger problem than the small, but real, number of “straight-up racists.”

Personal experiences and cultural background mean even well-meaning prosecutors can succumb to stereotypes, said Pearson, who spent 14 years as a prosecutor in Miami and now works for the American Civil Liberties Union of Florida.

She said this problem, part of what some call “implicit bias,” can be overcome by training and policies to help achieve an objective analysis.

Cyrus Vance Jr., the Manhattan district attorney, adopted one such policy, an aggressive training program after a 2014 report by the Vera Institute of Justice found racial disparities in the outcome of prosecutorial decisions.

When announcing the report, with which his office cooperated, Vance said he was “committed to implementing preventative strategies to reduce any unintended racial and ethnic disparities.”

The office requires every prosecutor and staffer to take multiple classes on recognizing “implicit bias” and combating its results.

Without looking at prosecutors’ and the police’s unconscious prejudices, Pearson said, racially biased outcomes are inevitable.

“Ignorance is not bliss,” she said.

Methodology

The Marshall Project requested data from the FBI’s Supplementary Homicide Report and received records detailing close to 600,000 homicides from 1980 through 2014. The analysis focused on 400,000 cases where information about the killer was available.

The police data do not necessarily reflect the final outcome of a case, which is determined by prosecutors and the court system and does not always get reported back to the FBI. For instance, Trayvon Martin’s death is listed as simply “other,” not as “justifiable,” though his killer was later tried and acquitted. That could mean that “justifiable” cases of all kinds are underreported.

The data entered by police are incomplete; not all police departments participate and not all states collect the same data. In some cases, particular states did not report data on justifiable homicides. The Marshall Project separately collected data from Florida, which has not provided homicide data to the FBI since the mid-1990s. In another example, New York State failed to collect and report data on any justified homicides from 2007 through 2014. However, despite the gaps and problems, when jurisdictions with inconsistent data were removed from the equation the racial disparities remained.