Mark Hughes was marching in peaceful protest, his rifle strapped to his chest in a demonstration in Dallas, when the deadly sniper shots first split the air. Hundreds of fellow activists scattered.

Then Hughes learned he was a "suspect," misidentified as such by Dallas police in a tweet Thursday night featuring a photo of him in a camouflage shirt.

Hughes was cleared soon after. He voluntarily handed his firearm to officers amid the chaos after the ambush shootings of 12 police officers, five of whom died.

But that was not before Hughes's name came to be linked with the tragedies of Philando Castile and Alton Sterling, the two latest black men to have died in back-to-back U.S. police shootings that sparked outrage across the country and beyond this week.

Among the common threads connecting Hughes to the two dead men? Gun ownership. More specifically, being a gun owner with black skin — an experience that puts a tinge of racial animus on the African-American community's right to bear arms, say social justice advocates.

Both Castile and Sterling were reportedly carrying firearms when they died by police gunfire.

Hughes carried his weapon to the Dallas protest over their killings, a legal right enjoyed by many gun enthusiasts in the state of Texas. But legal or not, there's just something about the idea of black men carrying openly that arouses another level of suspicion, says Maryland political consultant Neal Carter.

"Texas is an open carry state," tweeted Carter, who often comments about racial issues. "If Mark Hughes was white, you would be silent."

Carter said he was reminded of a video social experiment contrasting treatment of two purportedly legal gun owners, a white gun owner carrying an AR-15 rifle down an Oregon street, versus a black man doing the same. The white man was politely questioned by police. The black man was held at gunpoint by an officer, ordered to lie down in the street, then detained.

Open carry is generally legal in the state of Oregon. It's also the law in Louisiana, where Sterling was killed on Tuesday around 12:35 a.m.

Sterling was shot following an altercation with police in a Baton Rouge parking lot where he was selling CDs. The encounter escalated quickly, after two white officers responded to a 911 call about a man brandishing a gun.

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Diamond Reynolds weeps after she recounts the incidents that led to the fatal shooting of her boyfriend Philando Castile by Minneapolis area police during a traffic stop on Wednesday, at a Black Lives Matter demonstration in St. Paul, Minn. (Eric Miller/Reuters)

Videos of the incident show the 37-year-old being pinned to the pavement, then shot multiple times after someone shouts that Sterling has a gun.

The next day, Castile was shot to death in his car in Falcon Heights, a suburb of St. Paul, Minn., apparently while he was reaching for his wallet to show an officer his licence and registration. The 32-year-old is said to have had legal permits to carry his weapon.

Anthony Newby believes the tragedies expose discomfiting truths about precisely who America's Second Amendment is meant to protect.

"Mostly white men," says Newby, who heads the anti-violence Minneapolis group Neighborhoods Organizing for Change.

Second Amendment advocates, he says, often characterize the right to bear arms as a way "to protect themselves and their property."

"But when those same guns are extended for the self-preservation of black and brown bodies," Newby says, "you see a direct contrast."

President Barack Obama spoke out about the shootings, calling them a disturbing pattern that was "symptomatic of a broader set of racial disparities" in the U.S. criminal justice system.

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Lakeith Howard demonstrates outside the Triple S Food Mart where Alton Sterling was shot dead by police in Baton Rouge, Louisiana. (Jonathan Bachman/Reuters)

At a news conference Thursday, Minnesota Gov. Mark Dayton also acknowledged possible discrimination at play.

"Would this have happened if those passengers, the driver were white?" he asked. "I don't think it would have."

The governor added that no one should have paid with their life for a broken tail light.

"I can't say how shocked I am and deeply, deeply offended that this would happen to somebody in Minnesota," he said.

According to Castile's girlfriend, who was in the passenger seat during the incident, allowing her to broadcast the bloody aftermath over Facebook Live, the school cafeteria worker had informed the officer that he had a concealed weapon with a permit.

Reynolds said he was reaching for his identification when the officer opened fire.

"Not one shot, not two shots, not three shots, not four shots — but five shots!" she said at an emotional news conference outside the governor's mansion.

Sterling's case is more complicated, by virtue of his rap sheet.

The father of five lived in an open-carry state, meaning Louisiana residents can publicly carry firearms so long as they have the proper permits. Court records show Sterling pleaded guilty in 2011 for possession of a firearm and illegally carrying weapons, which should have precluded him from carrying a gun legally.

Implicit bias

Even so, it's unclear whether the two white officers who tackled him before he was shot would have had that prior knowledge. Had they not known about his criminal history, critics argue, Sterling's possession of a firearm should not have been reason enough for police to use lethal force.

John Crawford III was killed in an Ohio Walmart in 2014 while holding a toy BB gun he picked up while shopping. Activists note that if the gun were real, police still would not have had reasonable cause to stop him because of Ohio's open-carry status.

But such cases are why black leaders point to research suggesting police may be implicitly biased toward minorities, or view them as a greater threat than their white peers.

A new study on police use of force that parsed data from Washington Post news reports found that among citizens fatally shot by police in 2015, black citizens "were significantly more likely to have been unarmed than white citizens," says study co-author Justin Nix, with the University of Louisville's Department of Criminal Justice.

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Relatives and friends identified the man shot by police in St. Paul, Minn., as 32-year-old Philando Castile. (Philando Castile/Facebook)

"This, we believe, is preliminary evidence of implicit bias," Nix says.

Blacks are also over-represented as victims of police killings, according to Amnesty International's 2015 Deadly Force report. While African-Americans represent 13.2 per cent of the U.S. population, they accounted for 27.6 per cent of total deaths at the hands of police between 1999 and 2013, the study said, citing figures from the U.S. Centers for Disease Control.

Underlying all of this is anxiety over self-preservation, stemming from a long history of slavery, says Jeff Hassan, of the African-American Leadership Forum, in St. Paul.

Black sons and 'The Talk'

"I have three sons, one of whom has serious mental health issues, and his mother and I are in constant fear that he'll have an encounter with a police officer, not knowing he has a mental health issue," says Hassan, who has litigated several police misconduct cases involving black victims. "These are conversations we have. What can parents tell their children to keep them super-safe?"

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A crowd gathers at the scene of the police shooting in Falcon Heights, Minn. (Leila Navidi/Star Tribune via Associated Press)

Black families refer to the disquieting ritual as "The Talk," a discussion about respectful conduct with police, lest a confrontation turn deadly.

But following the rules evidently isn't enough to protect black lives in America, says Steve Belton, president of Minneapolis Urban League. Not as long as implicit bias is in play.

"In the eyes of the law, if you're an African-American with a gun, you're a threat," he says. "Even if you have a legal permit to have that gun."

Belton, whose sons are now 25 and 28, recalls having the talk with his boys when they were as young as 12.

"You tell them to anticipate puberty coming, these changes happening to your body. But it's also a talk about what happens in terms of societal puberty," he says. "You become a changed person in the eyes of the world. You tell them that, in the eyes of law enforcement, you are soon to become one of the most dangerous men in the world. And it's not your fault."