The assault went on for hours, until Chicago police found the disoriented victim walking along a street, authorities said.
The suspects, who were jailed, can be heard on the video using profanities against white people and President-elect Donald Trump.
Police spokesman Anthony Guglielmi said investigators initially concluded that the 18-year-old man was singled out because he has "special needs," not because he was white. But authorities later said the charges resulted from both the suspects' use of racial slurs and their references to the victim's disability.
It's also possible that the suspects were trying to extort something from the victim's family, police said. The man's parents reported their son missing Monday and told authorities they later received text messages from people who claimed to be holding him captive.
The victim was a classmate of one of the attackers and initially went with that person voluntarily, police said.
"He's traumatized by the incident, and it's very tough to communicate with him at this point," police Cmdr. Kevin Duffin said.
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 victim does not appear to make any attempt to defend himself or to escape his attackers. He is a suburban Chicago resident described by Police Superintendent Eddie Johnson as having "mental health challenges."
"There was never a question whether or not this incident qualified as being investigated as a hate crime," Johnson said. But "we need to base the investigation on facts and not emotion."
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 incident began Dec. 31, when the victim and one of the suspects, 18-year-old 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 Cmdr. Kevin Duffin said.
The victim told police what began as playful fighting escalated, and he was bound, beaten and taunted with racial slurs and disparaging comments about his mental capacity.
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 obviously disoriented man wandering down a street.
The man was bloodied and wearing a tank top that was inside-out and backward. He had on jean shorts and sandals, despite freezing weather, officer Michael Donnelly said.
Most hate crimes are connected to the victim's race, but hate-crime charges can be sought in Illinois if a victim's mental disability sparked an attack, though it is rare.
In addition to hate crimes, the four were charged with kidnapping, aggravated battery and aggravated unlawful restraint. Three were also charged with burglary. It was unclear whether any of the suspects had attorneys. They were to appear in court Friday.
Family members of the victim spoke briefly to reporters Thursday at a suburban hotel but declined to comment on the allegations or the investigation.
Neal Strom, who is acting as a family spokesman, told The Associated Press that the victim has had "profound emotional and physical disabilities throughout his life." He did not elaborate.
Cook County prosecutors identified the suspects as Brittany Covington and Tesfaye Cooper, both of Chicago, and Hill, of suburban Carpentersville. All are 18. A fourth suspect was identified as Covington's 24-year-old sister, Tanishia Covington, also of Chicago.
The grandmother of Brittany Covington said the granddaughter she raised from infancy is "not this person."
"I'm so upset, my head is about to bust open," said Priscilla Covington of Chicago. "I don't know if someone influenced her ... She had her ups and down. (She) was a good person. I'm so confused."
In Washington, White House press secretary Josh Earnest said the beating demonstrated "a level of depravity that is an outrage to a lot of Americans." He said he had not yet spoken to President Barack Obama about the attack in the president's hometown.
The video emerged at a time when police dealings with Chicago's black community are being closely watched. Less than a year ago, the nation's third-largest police force was sharply criticized by a task force for using excessive force and honoring a code of silence.
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.
(AP)
This booking photo provided by the Chicago Police Department shows
Jordan Hill, of Carpentersville, Ill. Hill is one of four people charged
Thursday, Jan. 5, 2017, with aggravated kidnapping and taking part in a
hate crime after allegedly beating and taunting a man in a video
broadcast live on Facebook.
