CHICAGO — The two 18-year-old men had been schoolmates, police said. After meeting at McDonald’s, they spent two days together, driving around visiting fr...

CHICAGO — The two 18-year-old men had been schoolmates, police said. After meeting at McDonald’s, they spent two days together, driving around visiting friends. Then a pretend fight escalated into a brutal beating of one of the men, a mentally disabled teenager, in an attack that stirred racial tensions and outrage after being broadcast on Facebook Live.

How the white suburban teenager ended up beaten by the four black suspects, threatened with a knife and taunted with profanities against white people and President-elect Donald Trump is among the puzzles authorities are still trying to piece together after the suspects were charged with hate crimes.

The alleged attackers will make their first court appearance Friday, a day after they were also charged with kidnapping and battery in connection to the attack. The beating was captured on cellphone video by one of the assailants and has since viewed millions of times on social media.

“This should never have happened,” David Boyd, the victim’s brother-in-law, said at a brief news conference in suburban Chicago. He said the victim was traumatized but doing as well as could be expected.

Neal Strom, a family spokesman, told The Associated Press the victim has had “profound emotional and physical disabilities throughout his life.” He did not elaborate.

Police said drug use may have been involved in the incident. The video shows the two female suspects smoking cigars that authorities “presume to be blunts” while the victim is tied up and racial slurs and references “to his mental capacity starts coming out,” Chicago Police Commander Kevin Duffin said.

The uproar over the beating has intensified the glare on Chicago after a bloody year of violent crime and protests against Mayor Rahm Emanuel and a police department that has been accused of brutality and hushing-up wrongdoing. The department has also been the subject of a long civil-rights investigation by the Justice Department, which is expected to report its findings soon.

The incident also stirred emotions still raw after a nasty presidential election campaign that split the nation. The case heightened political tensions on social media, with some conservatives suggesting it was linked to the Black Lives Matter movement. Police said there was no indication of any connection.

The cruelty of the attack and the intense social media exposure prompted President Barack Obama to respond, calling it “despicable.”

“I take these things very seriously,” he told Chicago’s WBBM-TV on Thursday. He said the incident does not mean that race relations have gotten worse.

“We see visuals of racial tensions, violence and so forth because of smartphones and the internet and media … a lot of the problems that have been there a long time,” he said.

Chicago police initially said the youth was singled out because he has “special needs,” not because he was white. Authorities later said the charges resulted from both the suspects’ use of racial slurs and their references to the victim’s disability.

Cook County prosecutors identified the suspects as Brittany Covington and Tesfaye Cooper, both of Chicago, and Jordan Hill, of suburban Carpentersville. All are 18. A fourth suspect was identified as Covington’s 24-year-old sister, Tanishia Covington, also of Chicago.

Excerpts of the video posted by Chicago media outlets show the victim with his mouth taped shut and slumped in a corner of a room. At least two assailants are seen cutting off his sweatshirt, and others taunt him off camera. The video shows a wound on the top of the man’s head. One person pushes the man’s head with his or her foot.

A red band also appears to be around the victim’s hands. He was tied up for four to five hours, authorities said.

The incident began New Year’s Eve, when the victim and alleged assailant Jordan Hill met at a suburban McDonald’s to begin what both the victim and his parents believed would be a sleepover, police said.

Instead, Hill drove the victim around in a stolen van for a couple of days, ending up at a home in Chicago, where two of the other suspects lived, Detective Commander Kevin Duffin said.

The victim told police what began as playful fighting escalated. A downstairs neighbor who heard noises threatened to call police. When two of the suspects left and kicked down the neighbor’s door, the victim escaped. A police officer later spotted the bloodied and obviously disoriented man wandering down a street.

The victim’s parents reported him missing Monday evening, two days after last hearing from him. The police report said the victim’s mother knew the first name of her son’s friend — Jordan — but wasn’t clear on his last name. The report also noted that the victim “does not like telling his parents who he’s with.”

The parents later received text messages “from persons claiming to be holding him captive,” police said. While investigating the messages, police discovered the Facebook video.

The grandmother of Brittany Covington said the granddaughter she raised from infancy is “not this person.”