FBI agents arrested three former Alabama prison guards on Monday after a federal grand jury indicted them on charges of beating a handcuffed prisoner to death and lying to investigators about the attack.

Michael Smith, 37, Matthew Davidson 43, and Joseph Sanders, 31, former guards at Ventress Correctional Facility in Clayton, Ala., are accused of assaulting Rocrast Mack, a 24-year-old Ventress inmate, and making false statements to state and federal investigators about the attack after his death.

Mack was sentenced to 20 years in state prison after pleading guilty to selling $10 worth of crack cocaine to an undercover cop in 2009.

The fatal beating occurred Aug. 4, 2010, after a female guard, Melissa Brown, accused Mack of looking at her inappropriately while she did evening rounds in one of the prison's crowded dorms. Prison records obtained by the Huffington Post during a 2011 investigation into Mack's death showed that Brown struck Mack, slapping him across the face, then called for assistance after he struck her, bloodying her lip.

Smith, Davidson and Sanders responded and severely beat Mack in several areas of the prison using their feet, fists and batons, the indictment says. During part of the beating, Mack was handcuffed.

After a comatose Mack was taken to an outside hospital, Smith, Davidson and Sanders conspired to create a story that the beating was done in self-defense in an effort to restrain an out-of-control inmate, authorities said. In written reports and interviews with state and federal investigators, the officers claimed that Mack had been fighting them and resisted efforts to subdue him.

Smith also faces state murder charges for his role in the attack on Mack. He faces up to life in prison or the death penalty if convicted on all counts, while Davidson faces up to 105 years in prison and Sanders, 75 years.

State authorities initially described Mack's death as an "isolated incident" but ultimately acknowledged that Smith had been accused of brutality by numerous inmates. The Huffington Post investigation of Mack's death uncovered allegations of repeated brutality by Smith and other guards at Ventress that had gone unchecked.

Monday's indictments come as Alabama authorities struggle with the management of one of the most overcrowded and understaffed prison systems in the country. The state's prisons are at 193 percent capacity, the highest rate in the country, according to the Alabama Department of Corrections.

Some Alabama lawmakers warn that the state risks a mass release of inmates if conditions do not improve. In 2010, the Supreme Court ordered California to release about 30,000 inmates after its prisons reached 170 percent capacity.

Alabama lawmakers have long resisted calls to increase funding for the state's sprawling prison system, which grew by 468 percent between 1977 and 2009, due largely to a surge in drug-related arrests and the stiffening of prison sentences by state lawmakers.

Critics of Alabama's justice system allege that overcrowding is responsible for high levels of guard abuse, brutality and inmate-on-inmate violence in the state's prisons. Ventress, where Mack was killed, was one of the most crowded facilities in the state, at 225 percent of capacity.