MEMPHIS (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 wasn't 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 U.S. 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 Jan. 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 6 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 incentivize" the other officers to consider plea deals too. Mills will also cooperate in the U.S. Department of Justice's investigation in the Memphis Police Department, which Mulroy said should lead to systemic reform.

Mulroy said the defendants hold "different levels of responsibility" in Nichols' death and that Mills "is not the worst of the five" officers charged.

The plea agreement sets out Mills' role in the fatal beating, detailing how he pepper-sprayed Nichols three times before pulling out a baton and yelling, "I'm about to baton the (expletive) out of you." He repeatedly struck Nichols, who was on the ground and surrounded by officers, never giving him an opportunity to comply with the command, "give us your hands!"

After the beating, Mills and the other officers failed to tell the responding medics that they had beaten Nichols, instead saying he was on drugs. Meanwhile, among themselves they discussed "taking turns hitting Nichols, hitting Nichols with straight haymakers, and everybody rocking Nichols. During these conversations, the officers discussed hitting Nichols to make him fall and observed that when Nichols did not fall from these blows, they believed they were 'about to kill' him," according to the plea agreement.

Martin used hand signals to indicate to Mills that his body camera was still recording. Mills removed the camera and placed it on the back of a patrol car.

Mills told supervisors at the scene that he knew Nichols was in bad shape and he "expressed concerns about Nichols' survival," according to the agreement. When the five officers spoke later, they discussed what the body camera recording might show and conspired to mislead investigators. That included agreeing not to report that Martin had repeatedly struck Nichols in the head.

After Nichols' death, all five officers were fired from the department and the crime-suppression team they were part of was disbanded. The four remaining officers have a May 6 trial date in federal court. A trial has not yet been set in state court.

The officers said they pulled Nichols over because he was driving recklessly, but Police Chief Cerelyn "CJ' Davis said no evidence was found to support that allegation. Nichols ran from officers, who tried to restrain him. He pleaded for his mother as he was pummeled just steps from his home.

An autopsy report showed Nichols died from blows to the head, and that the manner of death was homicide. The report described brain injuries, cuts and bruises to the head and other parts of the body.

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Loller reported from Nashville.