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Four Chicago-area teens were being held Wednesday after a shocking Facebook Live video showed what appeared to be the beating and torturing of a bound and gagged man with mental health challenges while his attackers yelled anti-white expletives.

Chicago police said they expect to file charges Thursday against the four 18-year-olds — two men and two women — who were not immediately identified.

Police Superintendent Eddie Johnson called the video a "brutal act" that was "broadcast for the entire world to see."

"It’s sickening," Johnson said at a news conference Wednesday night. "It makes you wonder what would make individuals treat somebody like that. I’ve been a cop for 28 years and seen things that you shouldn’t see in a lifetime, but it still amazes me that you see things that you shouldn't."

Chicago police are questioning four teens after a Facebook Live video surfaced showing what appeared to be group of people beating a man who was tied up.

The video, which first aired Tuesday and was uploaded to YouTube, showed four young people kicking, slapping and cutting someone who is tied up on the floor in the corner of a room.

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The people could be heard yelling "F--- Donald Trump!" and "F--- white people!" at various points throughout the 30-minute video.

The victim attended the same school as one of the attackers, and may have gone willingly with the group from his Chicago suburb, officials said. They stole a van and brought the man to a location in Chicago, added Police Commander Kevin Duffin.

One of the four suspects allegedly recorded the brazen incident and allowed people to watch it in real time on her Facebook page.

The assailants in the video can be heard laughing, discussing drug use and putting the victim "out of his misery" and cursing the president-elect, while the bound victim moans through his gag.

Regarding the disturbing video that surfaced on social media of a battery: Incident is under investigation/suspects are being questioned pic.twitter.com/GGi3qs9rGv — Chicago Police (@Chicago_Police) January 4, 2017

A local police on patrol later found the victim disoriented while walking through a Chicago neighborhood, Johnson said. He was taken to a nearby hospital for his injuries and trauma.

"Thanks to the outstanding work of the 11th district police officers and area north detectives all four offenders from the incident are in police custody and awaiting formal charges," Johnson said. "The victim, who is not a Chicago resident, is currently recovering from the incident."

The four suspects had been arrested on unrelated battery charges later in the day, he said.

Investigators were then able to connect the two incidents through the Facebook Live video.

It took police most of the night to get the full story from the victim because he had such a difficult time communicating due to trauma, Duffin said. The young man was eventually able to explain what happened and has been released from the hospital.

CPD press conference regarding disturbing live social media video depicting a battery ; victim was tied up https://t.co/jDrjfz4sJV — Chicago Police (@Chicago_Police) January 5, 2017

“He was traumatized fairly good,” Duffin said. “It took most of the night for him to calm down and talk to us.”

The victim was reported missing from a Chicago suburb by his parents Monday night. He was with the group for at least 24 hours, if not longer, authorities said.

Police are investigating the case as a potential kidnapping and possible hate crime — the assailants in the video are black and called the victim a "goof-ass white man."

"We’re still investigating it, and if the facts guide us in that [hate crime] direction, then we’ll certainly charge them appropriately,” Johnson said.