A former Louisiana State Penitentiary guard already serving time for a sex crime admitted in federal court Tuesday that he beat a handcuffed Angola inmate in 2010 after the convicted killer tried to escape.

Mark David Sharp, 32, is the third ex-corrections officer to plead guilty to federal charges stemming from the beating of Roy McLaughlin, of Baton Rouge, who is serving a life sentence for the 1998 murder of his wife, Marianne.

Former Angola guards Kevin L. Groom Sr., who was a major at the prison, and Jason Giroir, who was a lieutenant colonel, previously pleaded guilty for their roles in trying to cover up the beating and are awaiting sentencing.

U.S. Attorney Walt Green said the investigation into the incident continues.

A shackled Sharp, with Assistant Federal Public Defender Mark Upton at his side, pleaded guilty Tuesday to deprivation of civil rights and making false statements to the FBI. He faces up to 15 years in prison and $500,000 in fines.

U.S. District Judge James Brady ordered a presentence investigation but did not set a sentencing date.

The beating occurred Jan. 24, 2010, in a prison van after McLaughlin tried to escape a third time. He was beaten with an extendable metal baton while his hands were handcuffed behind his back.

Giroir was driving and Groom was in the van when Sharp allegedly attacked McLaughlin, court records indicate.

Assistant U.S. Attorney Robert Piedrahita explained to Brady that Sharp told the FBI he didn’t strike McLaughlin.

Groom and Giroir both wrote in reports to the FBI that they didn’t see anyone attack McLaughlin in the van. In late 2011, all three men — Groom, Giroir and Sharp — told FBI investigators in interviews that they didn’t see anyone attack the inmate.

Groom pleaded guilty in 2012 to making a false report and making false statements. Giroir pleaded guilty last year to concealing and falsifying a federal document and making false statements.

Sharp, a former captain at Angola, was sentenced last year to three years in prison by a state district judge in St. Francisville following a conviction for felony carnal knowledge of a juvenile. He was arrested in 2011 after a 15-year-old girl who lived in the Angola employee housing area gave birth.