By early Tuesday afternoon, no one but Nia Wilson’s killer could know for certain why Wilson and her sister were singled out of the crowd, stabbed in the neck, and left for dead on a BART station platform Sunday evening.

But for many who mourned Wilson’s death, the evidence had already stacked up. The randomness of the attack, the rumored meeting of a white supremacy group in Oakland, and the races of a black victim and white alleged perpetrator all carried the trappings of a hate crime.

The trappings alone were enough. As soon as details of the attack spilled forth in the hours following the killing, the assumption by many on Twitter, many who protested, and at least one relative of the slain woman was that this was a racially motivated attack — despite statements as late as Tuesday afternoon from city leaders and investigators that such a motivation had not yet been proved.

HOW IS OAKLAND NOW SAFE FOR EVERYONE WHO FOR YEARS WERE TOLD THAT IT WAS A DANGEROUS PLACE, BUT NOW SOMEHOW *STILL* DANGEROUS FOR THE PEOPLE OF COLOR WHO ARE NATIVES???



PRAYERS FOR THE FAMILY OF #NiaWilson — WHIZ WARD (@yopotnawhiz) July 23, 2018

Even for Oakland, a city that has for years led the nation in protest rallies for racial justice after police shootings of African Americans, the swiftness of the assumption was jolting. And observers and experts are blaming that swiftness on a growing national atmosphere of racism that stretches from the shores of Lake Merritt all the way to the White House.

“President Trump is enabling racist people, plain and simple,” said Eva Paterson, an Oakland attorney who is founder of the national Equal Justice Society. “It used to be people felt shame for being a racist or saying the word ‘n—’. Not now.

“Now you have Charlottesville, where Trump says there were good people on both sides. You had the (Ku Klux) Klan endorsing Trump. And you have Trump putting children in cages at the border.”

Charlottesville, Va., is where a neo-Nazi rally last year led to the death of an anti-racism protester, and the cages Paterson referred to are detention centers for Latino immigrants along the Mexican border who were separated in recent months from their parents after entering the U.S. without permission.

But the problem, she said, is now everywhere, locally and nationally — as evidenced by the flap this spring when a white woman called police to complain about African Americans barbecuing at Lake Merritt. And last week, when the black owner of a high-end lemonade stand in the Mission District said someone called police on him, thinking he was breaking into his own business.

Now Playing: Now Playing People march in memory of woman slain on BART platform San Francisco Chronicle

BART police give update on Nia Wilson killing San Francisco Chronicle

BART police hold news conference on Nia Wilson homicide. San Francisco Chronicle

Paterson said that in this context, Wilson’s killing at the BART platform sent instant ripples of fear through her. The Wilsons are black, suspect John Lee Cowell — whose photo was released by BART police, and who was arrested Monday night — is white, and those two aspects by themselves, in context, spoke volumes to her.

“I thought, OK, now they’re (white-hate racists) killing us in Oakland — which is a city known for having black people,” Paterson said. “It just feels like they’re coming for us. It’s not paranoid. It’s objectively just looking at what is happening.”

Her fear was echoed by a Wilson family member, who posted a GoFundMe page asserting that Nia Wilson had been killed by a “White supremacy male.” The page had attracted more than $35,000 in donations by Tuesday evening.

“I feel like it was a hate crime,” said Wilson’s sister, Malika Harris, who posted the GoFundMe, and told The Chronicle, “I feel like there was some racist s— going on, but I really don’t know.

“I just don’t understand. Out of all the people on the BART, why her?”

Not everyone leaped to the same conclusion, even as they acknowledged the racial tensions.

In a statement issued Monday, Oakland Mayor Libby Schaaf said: “Although investigators currently have no evidence to conclude that this tragedy was racially motivated or that the suspect was affiliated with any hate groups, the fact that his victims were both young African American women stirs deep pain and palpable fear in all of us who acknowledge the reality that our country still suffers from a tragic and deeply racist history.”

In a meeting with reporters Monday afternoon, Wilson’s godfather Daryle Allums urged the community to “stand down” since no one knew the motives of the crime just yet.

On Monday evening, Allums, the leader of a movement based in Oakland that fights violence against children, wove with a megaphone through a protest called in reaction to the attack.

“Peace in the streets!” he yelled, over and over.

“We want peace, but we want justice — we don’t want no more blood on our hands,” he told The Chronicle. “If we send the community out there … it’ll be an old-school 1968-1970 civil rights war in Oakland right now. … So we just need the community to be on standby right now.”

Cat Brooks, a longtime rights activist and Oakland mayoral candidate who attended Wilson’s rally, said it would be irresponsible to ignore that the Proud Boys — described by many as a white supremacist group, although the group disputes that characterization — had reportedly planned a meeting in Oakland on Monday, but also irresponsible to flatly claim that the slaying and the meeting were connected.

However, she added that because of the current race and power dynamics in the city and country, it’s impossible to separate race as a factor when a white person commits an act of violence against a black person.

“There’s been a lot of debate around whether or not white supremacists or domestic terrorist organizations have the right to assemble and spew hate,” she said. “And what we consistently see, and what the data shows, is that hate speech incites hate crimes.”

The sentiment manifested Monday evening after the suspect’s arrest, when a planned vigil quickly evolved into the anti-racism protest and march. “No justice no peace” and “Say her name” chants erupted throughout the evening, and a crowd of about 1,000 marched from the MacArthur BART Station to downtown Oakland.

The march took a violent turn when demonstrators — seen in a video making the rounds on social media — began beating a man some believed to be a member of the Proud Boys. An Oakland Police Department spokeswoman said two people were detained after the incident and later released.

While removing them from the area, police said a portion of the crowd became disruptive and began throwing M-80 and M-1000 firecrackers at officers, injuring six of them. Officers deployed one chemical agent.

Proud Boys co-founder Gavin McInnes tweeted Tuesday that his organization had not planned a meeting Monday night in Oakland, and he denounced the attack that occurred during the march.

For the record.

1- Proud Boys are a multi-racial club.

2- Nia Wilson was not stabbed by a Proud Boy.

3- We NEVER planned to meet at @MakeWesting

You are attacking random strangers based on lies. #FakeNews #SayHerName — Gavin McInnes (@Gavin_McInnes) July 24, 2018

John Powell, director of the Haas Institute for a Fair and Inclusive Society, stressed that Wilson’s slaying didn’t happen in a vacuum, and black people are being harmed in large and small ways on a daily basis.

“If it’s not a stabbing or a shooting, it’s a barbecue,” he said.

Further, Powell said the crime appeared to be more calculated than random.

“It’s a white guy, it’s a black woman. ... He changed his clothes,” Powell said. “In other words, it didn’t seem just like a deranged person to me, it seemed more sophisticated.”

Powell noted that police face a lack of trust in the community, and said investigators should release as much information to the public as possible on Wilson’s case.

On Tuesday afternoon, BART Police Deputy Chief Ed Alvarez said there was still no evidence to charge Cowell, 27, with a hate crime. Alvarez said Cowell declined an interview with investigators. The suspect has a long, violent rap sheet.

“As of today, there’s nothing to substantiate that (hate crime) claim,” he said. “Our investigators go through everything — his histories, his criminal history, all that stuff. ... If there was anything there, that would come to our attention, and we would deal with it accordingly.”

Megan Cassidy and Kevin Fagan are San Francisco Chronicle staff writers. Email: megan.cassidy@sfchronicle.com, kfagan@sfchronicle.com Twitter: @meganrcassidy @KevinChron