Chicago authorities filed hate crime and other felony charges against the four on Thursday, with one White House spokesperson calling the video an "outrage."

A video of the assault, broadcast on Facebook Live by the attackers, shows an 18-year-old white man with special needs being beaten, verbally assaulted and cut. His assailants, all of whom are black, can be heard yelling "F--- Donald Trump" and "F--- white people" as he cowers in the corner of the room.

Besides hate crimes, authorities also charged the suspects - 18-year-olds Jordan Hill, Tesfaye Cooper and Brittany Covington, and 25-year-old Tanishia Covington - with kidnapping and battery.

It's still not clear if the victim was targeted for his skin color, his politics, his mental condition or for another reason.

'This is a sickness'

The video, which quickly went viral, has provoked a strong response from people across the country. White House Press Secretary Josh Earnest said it displayed "a level of depravity that is an outrage to a lot of Americans." Other critics, such as conservative media personality Glenn Beck, took to Twitter to tie the crime to the Black Lives Matter (BLM) movement, albeit without citing any evidence.

Civil rights leader Jesse Jackson responded with a statement, insisting the crime "has nothing to do with our social or civil rights struggle. This is a sickness and is widely rejected."

The victim, who is recovering after being released from the hospital, was found wandering in the streets after the assault. Police believe he was held in captivity for 24 to 48 hours and that he knew at least one of his kidnappers.

"It's sickening," said Chicago Police Superintendent Eddie Johnson after the four were initially taken into custody. "I've been a cop for 28 years, and I've seen things that you shouldn't see in a lifetime, but it still amazes me how you still see things that you just shouldn't."

blc/dr (AP, AFP, dpa)