Prosecutors have filed hate crime and aggravated kidnapping charges against the four people
Four people have been charged after a video showing a man with special needs being beaten and tortured was streamed live on Facebook.
Footage filmed in Chicago shows a woman laughing and smoking to camera as others use a knife to tear the victim's clothes and cut his hair until his scalp bleeds.
He is seen bound, gagged and slumped on the floor in a corner of a building during the ordeal.
At one point, one of the attackers kicks the helpless victim in the head.
Someone can be heard in the 30-minute video saying: "F*** Donald Trump" and "F*** white people boy."
Police have described the attack as "sickening", and prosecutors have filed hate crime and aggravated kidnapping charges against four people accused of being involved.
Jordan Hill, 18, Brittany Covington, 18, Tesfaye Cooper, 18, and Tanishia Covington, 24, have also been charged with aggravated unlawful restraint and aggravated battery with a deadly weapon.
CPD Arrested and Charged all four offenders with Hate Crime, as well as other charges, from West Side kidnapping and attack. Presser@2:15 pic.twitter.com/EoYnluf573— Chicago Police (@Chicago_Police) January 5, 2017
The victim is believed to have been held hostage for between 24 to 48 hours.
He knew one of the suspects from school, according to police.
Officers were called to a property on the city's West Side on Tuesday night and discovered signs of a struggle and damaged property.
At around the same time, officers on patrol found the victim on a nearby street.
Superintendent Eddie Johnson said the man, who has "mental health challenges", was recovering.
He was taken to hospital, but has since been discharged.
Police have said it is too early to say whether the attack was racially or politically motivated.
A spokesman for Facebook said it had removed the video because it does "not allow people to celebrate or glorify crimes" on the site.
President Barack Obama has condemned the attack.
He insisted racism has not gotten worse - but suggested it is now more visible.
"We don't benefit from pretending that racism doesn't exist and hate doesn't exist," he said. "The fact that these things are being surfaced means we can solve them."