The details -- from what sparked it, to how many died -- remain murky, and until recently, most Americans had never even heard of it.
But with each passing year, the horror of what happened in Tulsa, Oklahoma at the end of May, 1921, comes more painfully into view.
A Black teenager, Dick Rowland, entered an elevator in Tulsa on May 30, 1921. By multiple accounts, he may have tripped getting in and inadvertently grabbed the arm of a white teenage girl, then got scared, and ran off. Or, as a sheriff's report put it, he attacked her, then fled.
Rowland was arrested the next day, and a crowd of both angry whites and blacks gathered outside the courthouse where he was held, stoked by a headline in the local Tulsa Tribune newspaper: "Nab Negro for Attacking Girl in Elevator."
Shots fired outside the courthouse left ten whites and two blacks dead.
At the time, Tulsa was home to something that seemed wildly out of place in the post-slavery era South, something that might even seem out of a place today: a mostly black, economically thriving neighborhood called Greenwood, nicknamed the "Black Wall Street".
A mob of whites descended on Greenwood, and for about 16 hours laid waste to it. More than 1,200 homes were destroyed, along with 35 blocks of businesses, most burned to the ground.
Grainy footage of the aftermath shows smoldering shells of buildings and bodies in the streets. Dozens of people were confirmed dead, but historians agree the actual death toll likely reached into the hundreds, possibly to 300, with hundreds more injured.
None of the attackers was ever named or prosecuted, no court trials ever put the horror of the attack on any kind of record and white Tulsa simply moved on.
Reverend Robert Turner, pastor of Vernon AME church in Greenwood, has been helping keep the story of the massacre alive.
Inside the church are old photos of the part of the building that survived the destruction, before the church was re-built. Outside, there's a plaque that describes how the section that survived "is the only edifice remaining from the worst race massacre in American history."
It was then-President Donald Trump's trip to Tulsa in June of last year, around the anniversary of the massacre and the annual "Juneteenth" celebration, which recognizes the emancipation of the slaves, that touched off renewed interest in both events. But adding to the rawness of the moment was the death of George Floyd under the knee of a white Minneapolis police officer just days earlier.
"For Trump to come on this weekend, at this sacred time," Reverend Turner told me at the time, standing outside the church, "I just think it's totally ridiculous."
But with media from around the world arriving in Tulsa that weekend, Turner was happy to get out the word about the massacre. He has been fighting for years to secure reparations for descendants of the massacre victims, at the very least for the three survivors of the massacre.
One of them, Viola Fletcher testified before Congress earlier in May on the idea of reparations.
"I'm 107 years old and I have never seen justice," said Fletcher. "I pray that one day I will."
There has been a sea change on the idea of reparations since last year and in the Chicago suburb of Evanston, Illinois, the city council recently approved reparations for the Black residents who suffered decades of economic discrimination.
And what touched off the Tulsa riot is viewed in an entirely new context since last year: the claim that a white woman was attacked by a Black man. On the same day as Floyd's murder in Minneapolis, a white woman in New York's Central Park was caught on cell phone video calling police, claiming to be under attack by a Black man, a lie that saw the woman eventually charged with a crime, and which launched a nickname for others who try the same: "Karens".
And the initial police report on Floyd's death said he died from a medical incident, which was proven a lie by cell phone video and the conviction the ex-officer, Derek Chauvin, who was found guilty of second-degree murder in April.
In Tulsa last year, outside the Trump rally, a couple of white young men overheard me mention the Tulsa massacre and yelled out that it was not Tulsans who carried out the massacre, that it was radical outsiders -- the Ku Klux Klan -- that rolled into Greenwood.
Historians are clear that it was Tulsans who did the damage, and recently, the great grandson of Tulsa's founder, W. Tate Brady, himself a member of the Klan, reached out in local Tulsa media outlets, asking for reconciliation. Jeffrey Myers, 68, expressed remorse and said that his great grandfather "was on the wrong side of history".
In churches across Tulsa this weekend, there were prayers for peace and hope for an increased awareness. A couple of new documentaries on the massacre are now shedding even more light.
There was also some tension with the arrival of a Black, armed militia on Saturday demanding reparations for the massacre's victims.
But the seemingly lightning speed on awareness of the massacre in the past year, compared to the previous 99 years of its relative obscurity, brings hope to Reverend Turner.
"My prayer," Reverend Turner told me last year, "is that the more people are made aware about [the massacre] and Juneteenth, that we actually have a society that's more willing to make the changes needed to address the generational effects of them."