The ghost of Charles Stuart still haunts Boston.

Twenty-four years ago, this month, Stuart, faked a car jacking, killed his wife and unborn baby, and claimed a black man committed the murder. His lie sparked a months long random stop and frisk of every black man in Boston within sight of a policeman.

Now, the ACLU has analyzed police provided data from 2007-2010 documenting the stop and frisk practices of Boston police. ACLU concludes that Boston police “disproportionately observed, interrogated, and searched” black Bostonians. Even though the data is about seven years old, the results corroborate the ongoing complaints of local African Americans. Especially from young black men.

But the ACLU says, "The study shows evidence not just of racial disparity, but of racial bias.”

Commissioner Williams Evans responded saying the police department’s focus is on violence. He explained the BPD’s high rates of stop and frisk, what police officers call field interrogation and observation, is concentrated in high crime areas and in places where known gang members live. He did, however, admit that racial disparity in the ranks is real, despite promotions like that of William G. Gross, an African- American, who earlier this year was named BPD’s second in command.

One particular piece of the police data caught my eye. It backs up the ACLU’s claim of racial bias. Eight percent of African Americans without criminal histories or gang history were among those interrogated and observed. Young men like Ivan Richiez, who told the Boston Herald, he had  “been stopped too many times to count.” Richiez complained, “You’re treated based on their perceptions only.”

But, as we’ve seen recently when it comes to cops and black men, perceptions can be deadly.  I’ve spoken before about the killings of unarmed black men by cops who assumed the worst, even though there was no physical evidence to prove otherwise. This is what racial bias looks like, and the ACLU is right to call the Boston Police’s documented racial bias “alarming.”

Commissioner Evans points out that much has changed since 2011; well after the information for this study was conducted. BPD’s official response to the ACLU report is a detailed listing of how the department is tackling its culture, which led to racial disparity and bias. And, according to BPD, field interrogation and observation stops have dropped 42 percent since the time of the study, arrests by 33 percent.

And certainly the BPD should be commended for some recent efforts to head off potential racial tension—sitting down with teens of color after the killing of Michael Brown by Ferguson Missouri cop Darren Wilson.

There will be those who want to dismiss the importance of the ACLU study because the data is dated. It is dated, but the facts about unconscious bias playing a role in stops and frisks are sadly not outdated. When perception is dangerous reality, there is still much work to be done.