The shaky video shows a terrified young man in a gray hooded sweatshirt and dark pants crouching in a corner, his wrists and neck bound with orange bands, his mouth taped shut.
A young woman films as two young men slash the sleeves of his shirt with knives, then take turns punching him, slapping him and stomping on his head. At one point, one of the men can be seen cutting the victim's hair and scalp with a knife, and the victim is later shown bleeding from his injuries.
As the victim cowers with his back to the wall, someone can be heard repeatedly shouting, "f-- Donald Trump" and "f-- white people."
Throughout the 28-minute video - which focuses mostly on the young woman behind the camera - the group laughs, jokes and listens to music as the victim sits motionless on the floor. About halfway through, someone says the man "represents Trump," and threatens to put him in the trunk of a car and "put a brick on the gas."
It's unclear what happens to the victim when the video cuts off.
Chicago police on patrol said they found the disoriented victim walking down the street Tuesday in shorts, despite the frigid cold, and took him to the hospital for treatment. They said he was mentally disabled and appeared to be "in crisis." Shortly after, police said, they responded to a battery call at residence on the same block and took four suspects - two adult males and two adult females - into custody.
On Wednesday, those four people were being held on suspicion of abusing and torturing the man in a possible hate crime police say the group streamed on Facebook Live, which allows users to broadcast real-time events from their mobile phones and has increasingly been employed to air disturbing and often criminal conduct, along with personal rants, cat videos and hoaxes.
Police declined to give the race of the suspects or the victim. In the video, the suspects appear black. The victim appears to be white.
Chicago Police Superintendent Eddie Johnson said that the victim was an adult male with "mental health challenges." The suspects were in custody Wednesday and awaiting formal charges, which could include hate crime charges, Johnson told reporters in a news conference.
"The images in the video put on display the brazenness of the offenders who assaulted the victim and then broadcast it for the entire world to see," Johnson said.
"It's sickening. It makes you wonder what would make individuals treat somebody like that," he said. "It still amazes me how you still see things that you just shouldn't. I'm not going to say it shocked me, but it was sickening."
According to police, the victim lived in the Chicago suburb of Crystal Lake and was acquainted with one of the suspects through school. Police said the victim appeared to have voluntarily met up with the suspect he knew at some point and later rode with others in a stolen van to Chicago's West Side. He was with the suspects for at least 24 hours and maybe as long as 48 hours, police said.
Police in nearby Streamwood, Illinois, said the victim's parents had not heard from him since Dec. 31, when they dropped him off at a McDonald's in the area, according to the Chicago Sun-Times. After reporting him missing on Monday, police said, the victim's parents received "text messages from persons claiming to be holding him captive."
At about 5:30 p.m. Tuesday, shortly after police found the victim wandering in the street, officers were called to a battery at a residence in Chicago's Homan Square neighborhood on the city's West Side. There, they "discovered signs of a struggle and damage to the property and were able to link this evidence to the disoriented male," the department said in a statement.
After viewing a Facebook Live stream depicting "battery of an adult male," investigators said they concluded that the victim was the same person in the video. The department said that it believes the video is "credible."
Area North Detectives Commander Kevin Duffin said the department was weighing whether to bring hate crime charges against the suspects, saying it was not yet clear whether the attack was motivated by bias.
"They're young adults. And they make stupid decisions," Duffin said. "That certainly will be part of whether or not we seek a hate crime to determine whether this is sincere or just stupid ranting and raving."
Police are also trying to determine whether the attack constituted a kidnapping. When police found the victim, Duffin said, he was so traumatized that it took most of the night to calm him down to the point that he was able to talk to investigators.
"We're still talking to the victim. It's quite a possibility that it was a kidnapping," Duffin said. "But he's traumatized by the incident and it's very tough to communicate with him at this point."
Though he was badly shaken, the victim entered the hospital in "stable condition" and has since been released, police said. The extent of his injuries was not immediately clear, but a department spokesperson told the Sun-Times that he had suffered from cuts and burns.
The incident comes as violence in Chicago has reached record levels, with the homicide rate hitting a 20-year high in 2016. The issue has caught Trump's attention. Earlier this week, the president-elect called on Chicago Mayor Rahm Emanuel to seek federal help to address the 762 homicides and more than 4,000 gunfire victims last year. The city responded that the mayor and Trump had previously spoken about the issue.
This is not the first time in recent months that people in Chicago have been captured on video attacking someone while invoking the president-elect's name. In November, the day after the presidential election, a group of people were recorded beating a 49-year-old man while shouting, "you voted Trump" and "don't vote Trump." Four people were charged with vehicular hijacking in connection with that incident.