MEMPHIS, Tennessee (AP) — A former Memphis police officer pleaded guilty Thursday in the fatal beating of Tyre Nichols, becoming the first of five officers charged to reverse course, with prosecutors recommending up to 15 years in prison.

Desmond Mills Jr entered his plea during a hearing at the Memphis federal courthouse as part of a larger agreement to settle charges in state court as well. It was not immediately clear if any of the other officers would follow suit. Attorneys for three of the officers declined to comment and William Massey, the lawyer for Emmitt Martin, said in an email that they “will stay the course” with the former officer’s criminal defense.

Mills pleaded guilty to federal charges of excessive force and obstruction of justice and agreed to plead guilty to related state charges. Mills also agreed to cooperate with prosecutors. The final sentencing decision rests with the judge. Mills remains free on bail ahead of his May 22 sentencing hearing.

Nichols’ mother, RowVaughn Wells, shook as she described hearing how five large men beat her skinny son.

“This one today was very difficult for me because this was really the first time I actually heard somebody tell and say what they actually did to my son,” she told reporters outside the courthouse. “So, this was very difficult. But I’m hoping that Mr Mills, it was his conscience that allowed him to make this plea agreement, and not because of his lawyers telling him it was the right thing to do.”

Caught on police video, the beating of Nichols in January was one in a string of violent encounters between police and black people that sparked protests and renewed debate about police brutality and the need to for police reform in the US. The five former officers who were charged also are black.

Mills and four other former Memphis Police Department officers were charged in federal court with using excessive force, failing to intervene, deliberate indifference and conspiring to lie, as well as obstruction of justice after they were caught on camera punching, kicking and beating Nichols on January 7. He died three days later.

The five — Mills, Martin, Tadarrius Bean, Demetrius Haley and Justin Smith — pleaded not guilty to second-degree murder and other charges in state court. Mills is the first to agree to plead guilty.

Nichols’ mother and her husband said the possibility of 15 years in prison is “a start.” Nichols’ stepfather, Rodney Wells, noted that Mills has a family, with three children six-years-old and younger.

“Fifteen years is a long time with no parole,” Rodney Wells said at the news conference. “That’s going to affect his family, that’s going to affect him.”

Shelby County District Attorney Steve Mulroy said Mills’ cooperation “probably would incentivise” the other officers to consider plea deals too. Mills will also cooperate in the US Department of Justice’s investigation in the Memphis Police Department, which Mulroy said should lead to systemic reform.