By now the facts are well-known: Trayvon Martin was a 17-year-old young black man who, on Feb. 26, 2012, was walking home from a 7-Eleven in Sanford, Florida, with a bag of Skittles and a bottle of iced tea. George Zimmerman, a neighborhood watchman of white and Latino heritage, though advised by police not to pursue Trayvon himself, got out of his car carrying his 9-millimeter handgun. Allegedly after some confrontation, Zimmerman shot Trayvon dead.

Should we think about this horrendous incident as a random encounter, or does it teach us something about the politics of race and the persistence of racial bias in America today?

When Zimmerman first called the police about Trayvon Martin, he said: “There’s a real suspicious guy. This guy looks like he’s up to no good, on drugs or something. It’s raining, and he’s just walking around looking about.” Writer E.J. Graff termed this “Walking While Black.” In other words, Trayvon was presumed to be guilty of something nefarious simply because of the color of his skin.

Some who’ve listened to the tape of Zimmerman’s 911 call believe they heard him use an obscenity and a racial slur. But whether Zimmerman is an overt racist or not is largely beside the point. Focusing on relatively isolated instances of overt racism tends to obscure and excuse the very pernicious, very persistent reality of implicit racial bias that runs throughout our society — and very much shaped how the world saw Trayvon Martin and how the world sees President Obama still.

Most people don’t throw around racial epithets, let alone admit they do so to researchers. Yet we know that racial stereotypes still exist in America, leading scientists now to focus on implicit bias: unconscious mental shortcuts that we form based on our life experience as well as the stories, culture and history we absorb around us.