A group of prison guards are under investigation for an alleged beating that resulted in the death a mentally ill inmate.

According to his sister, Samuel Harrell was handcuffed, thrown to the ground, kicked, punched and stomped on, to the point where he stopped breathing. She says it occurred in April at the hands of about 20 prison guards at Fishkill Correctional Facility.

She says she received a phone call 15-20 minutes after the alleged beating telling her that Harrell was dead.

The sister's attorney says an autopsy revealed that Harrell had cuts and bruises on his body and died of cardiac arrhythmia after an "altercation with officers." His death was ruled a homicide.

The Department of Corrections and state police say a full investigation into Harrell's death is underway.

Despite the ongoing investigation, the Harrell family attorney says the guards allegedly involved have not been disciplined or suspended.