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."

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14 PHOTOS Man’s apparent torture streamed on Facebook Live See Gallery Man’s apparent torture streamed on Facebook Live A combination photo shows four people charged with felonies for the beating of a man with mental health issues, L-R top row: Brittany Covington, 18, Jordan Hill, 18, bottom row: Tanishia Covington, 24, and Tesfaye Cooper, 18, shown in Chicago Police Department photos released in Chicago, Illinois, U.S. January 5, 2017. (Courtesy Chicago Police Department/Handout via REUTERS) #BREAKING: Chicago Police tell FOX 32 that four people are in custody after man tied up, tortured on Facebook Live… https://t.co/J6nUXHzXty Chicago Police Commander Kevin Duffin, right, speaks during a news conference Thursday, Jan. 5, 2017 in Chicago, on the hate crime and other charges filed against four individuals for an attack on a man that was captured on a Facebook video. (Antonio Perez/Chicago Tribuen/TNS via Getty Images) Chicago police call the Facebook Live video attack "a brutal attack on an adult male with special needs" https://t.co/JALyjZ9h36 Jordan Hill, 18, one of four people charged with felonies for the beating of a man with mental health issues, is shown in this Chicago Police Department photo released in Chicago, Illinois, U.S. January 5, 2017. (Courtesy Chicago Police Department/Handout via REUTERS) Brittany Covington, 18, one of four people charged with felonies for the beating of a man with mental health issues, is shown in this Chicago Police Department photo released in Chicago, Illinois, U.S. January 5, 2017. (Courtesy Chicago Police Department/Handout via REUTERS) Tanishia Covington, 24, one of four people charged with felonies for the beating of a man with mental health issues, is shown in this Chicago Police Department photo released in Chicago, Illinois, U.S. January 5, 2017. (Courtesy Chicago Police Department/Handout via REUTERS) Tesfaye Cooper, 18, one of four people charged with felonies for the beating of a man with mental health issues, is shown in this Chicago Police Department photo released in Chicago, Illinois, U.S. January 5, 2017. (Courtesy Chicago Police Department/Handout via REUTERS) Four people in custody after Facebook Live video shows a man being tortured. "Fuck Donald Trump" can be heard… https://t.co/b5vxvvJXke Chicago Police Commander Kevin Duffin speaks during a news conference Thursday, Jan. 5, 2017 in Chicago, on the hate crime and other charges filed against four individuals for an attack on a man that was captured on a Facebook video. (Antonio Perez/Chicago Tribuen/TNS via Getty Images) CPD press conference regarding disturbing live social media video depicting a battery ; victim was tied up https://t.co/jDrjfz4sJV Chicago Police Superintendent Eddie Johnson speaks during a news conference Thursday, Jan. 5, 2017 in Chicago, on the hate crime and other charges filed against four individuals for an attack on a man that was captured on a Facebook video. (Antonio Perez/Chicago Tribuen/TNS via Getty Images) Regarding the disturbing video that surfaced on social media of a battery: Incident is under investigation/suspects… https://t.co/zpaCojhZH3 4 charged with hate crimes in torture of teen with special needs in Facebook Live video: https://t.co/10fYzkemao https://t.co/UrLU6C6uT7 Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

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.

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.

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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.

"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.

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