SAN QUENTIN (AP) — An investigation is underway to determine how drugs made it to death row at San Quentin prison in California, where two inmates died in their cells, corrections officials said Wednesday.

Officials were awaiting the results of an autopsy to determine if the deaths of Joseph Perez Jr. and Herminio Serna were related to drug use, according to a statement from the agency.

Corrections spokeswoman Terry Thornton declined to say what drugs were brought into the notorious prison north of San Francisco.

The statement says health care staff members at San Quentin are conducting outreach and education of inmates on the dangers of abusing illicit drugs.

Serna, 53, was found unresponsive in his cell on Monday. He was one of three men sentenced to death for killings committed during efforts by the Nuestra Familia gang to take over the drug trade in San Jose, authorities said.

Perez, 47, was found in his cell Tuesday and medical responders were unable to revive him.

He was sentenced to death for the 1998 killing of a woman who was stabbed and strangled during a robbery of her home in suburban Lafayette.

California has not executed anyone since 2006. Since 1978, when California reinstated capital punishment, 79 condemned inmates have died from natural causes on the nation’s largest death row. Another 25 have killed themselves and 15 have been executed.