Protesters associated with the Black Lives Matter movement were visible and vocal throughout the Democratic National Convention, but I'm not sure their message was heard above the din of Bernie Sanders supporters and other activists who took advantage of any opportunity to get in front of the TV cameras.

So many white people showed up for Tuesday's "Black Resistance March" that they were asked to retreat, reported Taylor Hosking, a Penn intern assigned to the Inquirer Editorial Board. "I need all white people to move to the back. This is a Black Resistance March," a Philly Coalition for R.E.A.L. Justice leader shouted over a loudspeaker. "And get that anarchist b— s— out of here. We are not afraid to kick people out."

The BLM marches and rallies haven't had as much impact as their antecedents during the civil rights era, which makes one wonder why a social-media-oriented movement that eschews the old-fashioned leadership of the Rev. Dr. Martin Luther King Jr. would rely on public demonstrations to ignite change. Like the Southern Christian Leadership Conference in King's day, the movement clearly craves media attention.

Tactics aside, the goal of ending biased treatment of minorities in police custody is important. Making that case during the convention were nine "Mothers of the Movement," including Gwen Carr, mother of Eric Garner, who was strangled by a policeman in Staten Island, N.Y.; Maria Hamilton, mother of Dontre Hamilton, who was shot 14 times by Milwaukee police; and Lesley McSpadden, mother of Michael Brown, who was shot and killed by a Ferguson, Mo., police officer.

Many of the points they made have been corroborated by the Sentencing Project, which for 30 years has pushed for reforms in the criminal justice system. In a report titled "Black Lives Matter," it used official data to conclude that more than half of those killed by police in recent years were black or Hispanic. Rarely were the officers involved convicted, or even indicted, for excessive use of force.

That insight was reflected in Wednesday's decision by Baltimore prosecutors to drop all remaining charges against police officers in the Freddie Gray case. Gray, 25, died after sustaining a neck injury while in police custody in April 2015. After three of the six officers charged in the case were acquitted, Baltimore State's Attorney Marilyn Mosby decided to drop the charges against the remaining three. She blamed "an inherent bias" among officers who would not betray fellow officers by cooperating with prosecutors.

The Sentencing Project's report includes a study that concluded black motorists are 31 percent more likely than whites to be stopped by police. Another study showed no apparent difference in who police stopped when a traffic law was broken. But it said 28 percent of black men under age 25 reported being stopped by police because they looked or acted "suspicious," compared with 13 percent of white men. The comparative rates were 17 percent for black women and 7 percent for white women.

Once pulled over, black drivers are three times as likely as whites to be searched, the Sentencing Project said, and twice as likely as whites to be arrested during a traffic stop. That disparity exists despite the fact that police generally find more "contraband" in white drivers' vehicles. The report also said blacks are three times as likely as whites to experience physical force by the police.

Bias can be found in other areas of the criminal justice system. The Sentencing Project cited studies showing prosecutors are more likely to charge minorities with crimes that carry heavier sentences, and that judges are more likely to give longer prison sentences to minorities than to whites accused of the same crime with a similar criminal history. Those statistics are reflected in the prison population, which is 37 percent African American. The total U.S. black population is only 13 percent.

Such numbers don't necessarily mean prosecutors and police officers are more biased than the rest of us. Many people, often inadvertently, act differently around people they don't know and may associate with stereotypes. But prejudice in the criminal justice system, especially by police, not only leads to inequitable treatment; as we have seen in Ferguson, Milwaukee, and Staten Island, it can also lead to death.

It's difficult to be a police officer in high-crime, low-income areas, which typically have large black populations because African Americans are disproportionately poor. Officers shouldn't assume the worst about people they have taken an oath to protect. Yet they can't be so naive as to drop their guard and put their own lives at risk. Knowing where to draw the line may take better training. It definitely should take removing officers who don't want to learn. But if officers do it right, their jobs will be easier and the communities they serve safer.

Harold Jackson is editorial page editor for the Inquirer.