On Sunday, a black undercover police officer came upon and engaged in a gun battle in Prince George's County, Maryland. Soon after, he was killed — not by one of the assailants who started the gunfight, but by a fellow police officer, Lynh Bui reported for the Washington Post.

The terrible tragedy immediately brought up worries of racial bias: Did a police officer shoot the undercover, plainclothes cop during the tense gun battle because he was black?

But Prince George's County Police Chief Henry Stawinski suggested it's not possible, the Post reported:

Stawinski said he was "uncomfortable with the notion that" bias would be "introduced to the conversation." He later clarified his response to the question about whether there was any suggestion of racial bias in the exchange of gunfire. "In those split seconds when lives are in danger and officers are engaging a deadly threat, there simply isn't time to bring any biases into it," Stawinski said. "Hindsight is a luxury that no officer has in the midst of an ambush."

The comments are alarming, because they get subconscious racial bias — a widely studied phenomenon also known as implicit bias — completely wrong. During split-second decisions, racial bias may in fact be the only factor that comes to mind: As a police officer reaches for his gun, aims for a target, and fires within seconds, the color of someone's skin is one of the quickest references that a racially biased cop may draw on to decide whether to shoot.

This is not an unfounded concern: There is plenty of research to support these worries about implicit bias.

Most people are at least a little racist, even if they don't know it

As part of a study published in the Journal of Personality and Social Psychology in 2014, researchers studied 176 mostly white, male police officers, and tested them to see if they held an unconscious "dehumanization bias" against black people by having them match photos of people with photos of big cats or apes. Researchers found that officers commonly dehumanized black people, and those who did were most likely to be the ones with a history of using force on black children in custody.

In the same study, researchers interviewed 264 mostly white, female college students and found that they tended to perceive black children ages 10 and older as "significantly less innocent" than their white counterparts.

"Children in most societies are considered to be in a distinct group with characteristics such as innocence and the need for protection," Phillip Goff, a UCLA researcher and author of the study, said in a statement. "Our research found that black boys can be seen as responsible for their actions at an age when white boys still benefit from the assumption that children are essentially innocent."

Other research suggests there can be superhumanization bias at work, as well, with white people more likely to associate paranormal or magical powers with black people than with other white people. And the more they associate magical powers with black people, the less likely they are to believe black people feel pain.

Another study found people tend to associate what the authors call "black-sounding names," like DeShawn and Jamal, with larger, more violent people than they do "white-sounding names," like Connor and Garrett.

"I've never been so disgusted by my own data," Colin Holbrook, the lead author of the study, said in a statement. "The amount that our study participants assumed based only on a name was remarkable. A character with a black-sounding name was assumed to be physically larger, more prone to aggression, and lower in status than a character with a white-sounding name."

Implicit bias likely influences police shootings

Implicit bias can also contribute to greater use of force by police. Studies show, for example, that officers are quicker to shoot black suspects in video game simulations. Josh Correll, a University of Colorado Boulder psychology professor who conducted the research, said it's possible the bias could lead to even more skewed outcomes in the field. "In the very situation in which [officers] most need their training," he said, "we have some reason to believe that their training will be most likely to fail them."

Implicit bias helps explain one of the troubling disparities in America's criminal justice system: Black people are much more likely to be shot and killed by police. An analysis of the available FBI data by Vox's Dara Lind found that US police kill black people at disproportionate rates: Black people accounted for 31 percent of police killing victims in 2012, even though they made up just 13 percent of the US population. Although the data is incomplete because it's based on voluntary reports from police agencies around the country, it highlights the vast disparities in how police use force.

To end these kinds of racial disparities, researchers say that people and police officers need to be aware they exist. Once they know of their own biases, after all, it could become easier to keep them in check. (Indeed, Prince George's County previously told the Post that it planned to start an implicit bias program.)

So the fact that Prince George's County's police chief was apparently unaware of how implicit bias works isn't just alarming because it shows he's potentially uninformed; it also could make it much harder to address and fix such biases in the future.