A California inmate was discovered dead inside his prison cell, prompting state authorities to conduct an investigation with the initial belief that the case is a homicide.

Officials said prison staff discovered the 29-year-old prisoner unresponsive at around 11:30 p.m. on Sunday. The victim was being held at High Desert State Prison in northeastern California near the Nevada border, the California Department of Corrections and Rehabilitation said.

Mysterious Inmate Death

Prison personnel was alerted by the victim’s cellmate, who told them the victim was not responding to him. Staff immediately conducted life-saving measures to resuscitate the man but were unsuccessful. Correction officials said the man was pronounced dead after about half an hour.

The victim was brought to the High Desert State Prison in 2018 after San Francisco County authorities sentenced him for seven years for charges of assault with a firearm.

Officials identified the victim’s cellmate as Erik S. Montes, who was named as a suspect in the case and was immediately placed in separate housing. The suspect was a notorious and respected gang member who was serving nearly three decades in jail.

Montes was arrested and charged for second-degree attempted murder with enhancement as well as possessing a deadly weapon while inside prison, said authorities, US News reported.