CHICAGO — The two 18-year-old men had been schoolmates, police say. 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 teen ended up beaten by four black people, 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 four were charged with hate crimes.

The alleged attackers will make their first court appearance on Friday, a day after they were charged.

The four also face charges of kidnapping and battery in connection to the attack, which was captured on cellphone video by one of the assailants and 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.