MONTGOMERY, Ala. - The last of four former Alabama prison employees charged in connection with an inmate beating death pleaded guilty Monday to one count of obstructing justice.

Former Ventress Correctional Facility officer Joseph Sanders entered the plea Monday after jury selection began for his federal court trial in Montgomery. Sanders admitted he lied when he told investigators that he didn't see a baton in a prison office where inmate Rocrast Mack was beaten on the night of Aug. 4, 2010, defense attorney Jim Parkman said.

"He did know about a baton being used and he lied," Parkman said.

The defense attorney said federal prosecutors offered his client a plea deal that was too good to turn down, and it included dropping other charges, including conspiracy and violating Mack's constitutional rights by hitting him.

U.S. District Judge Myron Thompson set sentencing for Sept. 23. Sanders faces up to 20 years in prison. Parkman said his client hopes to get less because he didn't lie to get somebody off. He said the reason for the lie will come out later.

Sanders, 32, had faced up to 75 years in prison if convicted of all charges against him.

A federal and state investigation began soon after Mack died. It found that Mack was beaten repeatedly in the prison yard, a prison office and the prison infirmary by prison employees. He died the next day at a Montgomery hospital with severe bruises from his head to his legs, his front two teeth knocked out, and his brain swollen from the blows.

Former officers Matthew Davidson and Scottie Glenn pleaded guilty earlier to violating Mack's rights and conspiracy. Former Ventress supervisor Michael Smith was convicted last month of violating Mack's rights by fatally beating him, conspiracy and obstructing justice. Testimony in the trial showed Smith beat Mack repeatedly with a baton in a prison office and stomped on his head.

U.S. Attorney George Beck said most correctional officers perform their jobs ethically. "However, these officers allowed a restrained man to be savagely beaten and stomped and then tried to cover it up. There is no excuse for such behavior. Hopefully, this plea will bring the Mack family some peace in knowing that no one is above the law," Beck said.

Mack was 24 when he died. He had been at Ventress since March 2010 on a 20-year sentence for a drug conviction in Montgomery County. His family sued the state over his death and got a $900,000 settlement.

The case began when a female officer hit Mack in his bed and he struck her back. She radioed for help, saying an inmate had jumped her.