A second former Memphis police officer has pleaded guilty to federal charges in the death of Black motorist Tyre Nichols, whose videotaped beating by five Black officers in January 2023 shocked the United States.

Emmitt Martin pleaded guilty to two of four federal counts against him – one for depriving Nichols’s civil rights and another for witness tampering – according to his plea agreement filed in a US district court in the state of Tennessee on Friday.

Sentencing has been set for December 5.

Nichols’s mother, RowVaughn Wells, who was in the courtroom on Friday, said the hearing was “very emotional” and “bittersweet”.

The latest plea was a step in the right direction, she said but added that she will not be content until all of the officers are brought to justice.

Martin agreed to cooperate with the investigation, raising the possibility of him testifying against fellow former officers as he admitted to conspiring with the others to provide a misleading account of the beating.

Martin is also expected to plead guilty to related Tennessee state charges, the Shelby County district attorney’s office said in a statement on Friday.

In November, another former Memphis police officer, Desmond Mills, pleaded guilty to federal charges and agreed to plead guilty to related Tennessee state charges. In exchange, Mills, who was facing life in prison, agreed to a 15-year sentence with state and federal prosecutors, the district attorney’s office said at the time.

Under Martin’s deal, federal prosecutors agreed to recommend a sentence of no more than 40 years.

Martin and Mills were among five officers who had previously pleaded not guilty to federal civil rights offences and state charges of second-degree murder.

The federal trial is scheduled to begin on September 9. The state trial is on hold while the federal case develops.