A peaceful vigil was held at Meridian Hill Malcolm X Park in Northwest Washington D.C., on Thursday. A national moment of silence was observed in honor of 18-year-old Michael Brown, who was shot and killed by police last weekend, and victims of police brutality. (Ben Dorger/The Washington Post)

“Oh, it can happen here,” declared the 34-year-old mom watching her son climb a fence, warning him that she does not want another summer of stitches. “Anywhere the police don’t treat people right, something like that can happen.”

On front porches across Barry Farm, a public housing complex in Southeast Washington, folks are talking about the shooting of an unarmed teen, followed by days of riots, in Ferguson, Mo. What happened there resonates here, especially among African Americans who have had tense encounters with police officers in the past.

“The police? We don’t know them. They don’t know us. We just stay. Out. Of. Their. Way,” said another woman, who, like everyone else I talked with, didn’t want her name in the paper if she was going to say what she thinks about the police.

But that shouldn’t be the case in D.C., where the police department has changed dramatically over the past 40 years. The nearly all-white force that a civil rights activist named Marion Barry called an alien “army of occupation” in 1970, just two years after riots ripped the city apart, became a department that mirrors the city’s demographics.

The current police chief, Cathy Lanier, is white and hugely popular across the city. In the past, though, we’ve had black police chiefs. Six of the seven police district commanders are African American, and the force is 58 percent black in a city that is now 50 percent African American.

So how could it be that some residents still feel vulnerable and at odds with the department when it looks so much like them?

Part of the powder keg that is erupting before the nation’s eyes in Missouri, after all, is the product of long-simmering racial tensions. Only two percent of the Ferguson police department is African American, in a town that is 65 percent black.

That kind of imbalance is the perfect stage for a police force to take on the role of an occupying army.

An academic study dating back to 1968 found that residents of 14 cities consistently had better relationships with police departments whose makeup reflected the community. A 2008 study compared the District with Chicago, where the majority-white police force was widely mistrusted by African American residents. The District scored higher in every category.

But there’s still plenty of mistrust — the kind that may have led to the gunfire that killed 18-year-old Michael Brown in Ferguson. Brown died in a scenario that every black parent in America faces and fears.

A lot of parents in the District call Ronald Hampton, who gives a little seminar on this subject about twice a month.

“It’s basically what to do if you’re stopped by police,” said Hampton, a former D.C. police officer who retired to a life of activism as executive director of the National Black Police Association after 23 years on the force. “This is a dinner table conversation that takes place in black homes; it doesn’t happen in white homes.”

Mostly he speaks to local African Americans after someone they know is pulled over, profiled or harassed. It happened to him, not long after he left the department.

“The officer told me, ‘You should’ve said you were a police officer,’ ” after Hampton chided him for profiling and for being rude and unkind. “It shouldn’t matter that I was a police officer. You just don’t treat people like this.”

When Hampton was on the force, the percentage of African American officers was even higher than it is now. We first talked back in 2000, when it was about 66 percent black and he was advocating for more leadership roles for black officers.

He has some fiercely held beliefs about how an officer should act on the job — white, black, brown, whatever.

“I talked to people, got to know them,” he said. That was called building “community capital,” and it paid off. “When I was out there, I didn’t hide. I stopped to talk to people. And if they didn’t want to talk to me because there was an awful police officer a while back, I told them not to judge me based on that officer,” he said.

Putting that much trust in people isn’t always easy for police officers. There’s a memorial wall honoring those killed just doing their jobs. Last year, a D.C. police officer, Scott Williams, was shot in both legs during the attack at the Washington Navy Yard.

That’s a lot of judgment to overcome on both sides.

At Barry Farm, residents I talked with said police officers wave at kids when they drive past but don’t engage with the adults. None of the two dozen people I talked with knew the name of any of the neighborhood cops. Didn’t want to know their names, either.

“Even if they did come up to me, I ain’t going to talk to them. Nobody’s telling them nothing,” said a 36-year-old mother of two, who said officers once searched her home the day before Christmas, ripping it apart, including gifts she’d wrapped for her older son. “I’m never going to forget that. They didn’t find a thing. And ever since then, I don’t trust police and my kids will never trust the police.”

A 41-year-old man sitting outside said that sometimes an officer will stop to talk with him but that he clams up. “I just stay out of their way. Don’t want nothing to do with them,” he said.

No wonder. He described being pistol-whipped by a police officer when he was a teenager. He was doing nothing but riding his bike between the apartments and the lines of laundry hanging out back.

It’s never easy to move past the sins of our country’s history. Especially when some of that history is only hours old and still being played out on Instagram.

That D.C. officer trying to strike up a conversation isn’t the cop who hit kids back in 1983.

That kid riding his bike isn’t every hooligan who’s wreaked havoc.

Just like Michael Brown, Trayvon Martin, Renisha McBride and Eric Gardner. They weren’t what others thought they were either.

Twitter: @petulad

For previous columns, go to washingtonpost.com/dvorak.