San Quentin inmate death being investigated as a homicide

Authorities with the California Department of Corrections and Rehabilitation are investigating the death of an incarcerated person at San Quentin Rehabilitation Center earlier this week as a homicide, officials said.

According to a press release issued by the CDCR , at 3:30 p.m. Tuesday afternoon, staff responded to an alarm and approached a cell occupied by Mark Squires and Gustavo Lopez. Arriving staff members said Squires was found unresponsive in his cell, and immediately called for facility medical assistance and outside first responders.

After initiating lifesaving measures on Squires, staff transported him to the prison's triage and treatment area where treatment continued. Medical personnel from an outside medical facility pronounced Squires deceased shortly after 4 p.m. Authorities said there were no other injuries to staff or other incarcerated individuals.

After the incident, Lopez was placed in restricted housing pending investigation by the San Quentin Investigative Services Unit and the Marin County District Attorney's Office. Squires' official cause of death will be determined by the Marin County Coroner.

Squires, 70, was most recently received at the facility from Riverside County in late January of 2000 to serve life with the possibility of parole for lewd or lascivious acts with a child under 14 with force or violence and failure to register/specific sex offense.

Gustavo, 36, was also received at San Quentin from Riverside County in January of 2020. He is serving more than 13 years for kidnapping and false imprisonment with violence among other crimes.