WATCH: Four black suspects charged in video beating of disabled white man in Chicago

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Four black people beat and taunted a mentally disabled white man in a video broadcast live on Facebook, threatening him with a knife, cutting off his clothing and forcing him to drink from a toilet.

The assault went on for up to two days, until Chicago police found the victim "in distress" walking along a street, authorities said.

Police spokesman Anthony Guglielmi said charges were expected to be filed later Thursday against the suspects, who are in custody. They can be heard on the video using profanities against white people and President-elect Donald Trump.

Authorities were reviewing whether the attack could be considered a hate crime, but initially they did not believe that the man was singled out because he was white.

Guglielmi acknowledged that the suspects made "terrible racist statements" during the assault, but he said the investigation showed that the victim was targeted because he has "special needs," not because of his race.

It's also possible that the suspects were trying to extort something from the victim's family, he said.

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 slumped in a corner as at least two assailants cut off his sweatshirt and others taunt him off camera. The video shows a wound on the top of the man's head, and one person pushes the man's head with his or her foot. A red band also appears to be around the victim's hands.

Off-camera, people can be heard using profanities about "white people" and Trump. At least one woman is shown in the video.

During much of the video, 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."

Johnson described the video as "sickening."

"It makes you wonder what would make individuals treat somebody like that," he said Wednesday at a news conference.

The grandmother of a young woman associated with the video 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."

The investigation began Monday after officers found a man "in distress" and "in crisis" walking on a street on the West Side, Capt. Steven Sasso said.

The man was taken to a hospital, and it was later discovered that he had been reported missing from an unidentified suburb.

At about the same time, police took several people into custody at a nearby address where they found signs of a struggle and property damage. Investigators determined that the missing man had been at the same address.

Asked Wednesday about the racial comments on the video, Duffin said the four people in custody were "young adults, and they make stupid decisions."

When considering a potential hate crime charge, investigators will have to determine whether the racial remarks were "sincere or just stupid ranting and raving," Duffin said.

Police have not identified the suspects, but said three are Chicago residents and one is from suburban Carpentersville. All of them are 18 or older.

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.