(Reuters) - The last of four defendants pleaded guilty on Thursday to taking part in a racially-charged 2017 attack on an 18-year-old mentally disabled Illinois man that was livestreamed on Facebook, county prosecutors said.

Tesfaye Cooper, 20, entered guilty pleas to one count each of committing a hate crime and aggravated kidnapping, said Tandra Simonton of the Cook County State’s Attorney’s Office.

The pleas were part of an agreement with prosecutors that saw additional charges dropped, Simonton said. Cooper is scheduled for sentencing on July 20.

Lawyers for Cooper could not immediately be reached for comment.

During the hearing Cooper issued a barely-audible apology to the victim’s family, the Chicago Tribune reported, after a letter was read in court from the victim’s sister describing the impact of the crime on his loved ones.

Cooper’s three co-defendants have already pleaded guilty in connection with the violent incident that took place in January 2017. It touched off an international furor after video of the livestream was circulated widely on social media and was condemned by then-President Barack Obama.

Police and prosecutors say the victim, who is white, was tied up for four or five hours by his African-American assailants, gagged and beaten, his scalp was cut and he was forced to drink toilet water.

In the video, the attackers could be heard making comments about “white people” as the victim cowered in a corner, his mouth taped shut.

At least one of the attackers could also be heard saying obscenities about Donald Trump, who was then president-elect. Police said they did not know whether the victim was a Trump supporter.

Jordan Hill, who prosecutors say led the attack, was sentenced to eight years in state prison last week after pleading guilty to similar charges.