The video showed a man in Chicago being tortured, and it was right there on social media for everyone to see.
As with other recent cases of live-streamed violence in the US, the reaction was swift, loud and highly politicized.
Chicago Police called the incident, first seen in a 30-minute Facebook Live stream, "sickening."
On Thursday, authorities filed hate crime charges against four suspects, all black, for an attack Tuesday on the victim, an 18-year-old white man. The victim, who police say has special needs, was shown backed into a corner, tied up with his mouth taped shut, and bleeding from his scalp as his hair was cut with a knife.
Following Wednesday's arrest of the four, the police were also investigating a second video that appeared on Twitter. This one showed the victim being forced to drink from a toilet at an apartment on the city's west side.
"Drink that s*** right f****** now," someone could be heard yelling while also making disparaging comments about US President-elect Donald Trump. "Drink the toilet water, b****! Say, 'F*** Trump!' Say, "F*** Trump!'"
That drew a strong reaction from the head of the city's police.
"The actions in that video are reprehensible," Chicago Police Superintendent Richard Johnson told reporters Thursday. Those actions or any kind of racism have no place in Chicago or anywhere else, he said.
Even President Obama weighed in Thursday, calling the video "despicable."
Facebook took down the video, though copies of it can still be found online.
"We do not allow people to celebrate or glorify crimes on Facebook and have removed the original video for this reason," a company spokesman said. "In many instances, though, when people share this type of content, they are doing so to condemn violence or raise awareness about it. In that case, the video would be allowed."
Twitter declined to comment for this story.
The incident marks the latest example of violence spilling live into social media feeds on the phones and PCs of people across the country and around the world. Over the past two years, Americans have borne witness to, among other incidents, the shooting death of Philando Castile during a traffic stop in Minneapolis; sniper attacks on police in Dallas; and, in June, a gang-related killing, also in Chicago.
In many of those cases, the human tragedy has led to visceral outbursts online and has inflamed debate over race relations.
Such outbursts occurred Thursday as the Chicago incident trended on both Twitter and Facebook.
Many on Twitter lashed out at the attackers, alleging that the violence was tied to the Black Lives Matter movement. The hashtag #blmkidnapping had a steady flow of uncompromising comments.
People with ties to Black Lives Matter dismissed any connection between that movement and the Chicago attack. Activist Deray McKesson said in a tweet that "It goes without saying that the actions being branded by the far-right as the 'BLM Kidnapping' have nothing to do w/ the movement."
Industry watchers say there needs to be some sort of oversight mechanism regarding social network posts.
"Social media platforms have not built what I call 'social intelligence,'" said Mark Babbitt, the co-author of the book "A World Gone Social." "We don't know where the lines are drawn to be good digital citizens.
Babbitt would benefit from oversight, referencing the Motion Picture Association of America for movie ratings.
In addition to the hate crime charge, each of the two men and two women in custody in Chicago faces criminal charges of aggravated kidnapping, aggravated unlawful restraint and aggravated battery with a deadly weapon.
Police say the victim had been reported missing for days after being dropped off by his parents at a suburban McDonald's on New Year's Eve to hang out with one of the suspects, whom he went to school with and considered a friend. That suspect allegedly picked up the victim in a stolen van and they drove to Chicago and hung out with people including the three other suspects.
The victim escaped just hours after the Tuesday attack and police found him wandering around traumatized after they responded to a disturbance involving the two female suspects. The police said they later made a connection to the Facebook Live video, in which the suspects can allegedly be seen in the background eating and laughing during the attack.
Kelley Heider, vice president of social media at SSPR, a San Francisco-based public relations agency, said the graphic videos provide "a moment of notoriety, clearly done for shock value and fame." She cautioned social media could breed more of these events "if they go unchecked."
Police said the victim may have been tortured for up to six hours.
"It makes you wonder what would make individuals treat somebody like that," Johnson told reporters. "I'm not going to say it shocked me, but it was sickening."
First published January 5, 4:16 p.m. PT.
Update, 6:46 p.m.: Adds comments from President Obama and social media experts.