The victim had bled to death from “multiple sharp force trauma injuries” and his body was mutilated in a jail cell in California.
A convicted killer beheaded another murderer in their prison cell and removed several of his body parts in a “sadistic” attack, it is alleged.
Jaime Osuna, 31, is accused of repeatedly cutting Luis Romero with a sharp object wrapped in string and attached to a handle at a jail in California.
Authorities believe the victim was alive for at least part of the attack which district attorney Phil Esbenshade described as the “most gruesome case” he had ever seen “in terms of heinousness in the slaying”.
Romero, 44, was found dead in his cell by guards at Corcoran state prison near Sacramento on 9 March.
He had bled to death from “multiple sharp force trauma injuries” and his body was mutilated, according to a post-mortem examination.
Osuna has been charged with murder, torture, mayhem and weapons possession.
The torture charge alleges he acted “with the intent to cause cruel and extreme pain and suffering for the purpose of revenge, extortion, persuasion and for a sadistic purpose”.
Osuna could face the death penalty as the killing “was especially heinous, atrocious, or cruel, manifesting exceptional depravity”.
He has appeared in court and has denied murder and other charges.
An investigation by the California Department of Corrections and Rehabilitation is under way.
Osuna has now been transferred to a prison in Stockton for inmates needing medical or mental health care, but officials have not revealed the reason for the move, citing privacy laws.
He was reportedly sentenced to life without parole after pleading guilty in 2017 to killing 37-year-old Yvette Pena at a Bakersfield motel in 2011.
Romero also was serving a life term for a Los Angeles County killing, but with the possibility of parole.