Dec. 6 (UPI) -- San Quentin State Prison officials in California held an emergency meeting Wednesday to discuss the deaths of two condemned inmates at the maximum security facility this week.
One inmate died Monday and another Tuesday. Two others also died recently, bringing the total to four in less than a month. Officials say they're looking at the possibility they died from overdoses of drugs smuggled into the prison.
The emergency meeting followed the death of Joseph Perez Jr., 47, on Tuesday and Herminio Serna, 53, Monday. The official cause of both deaths will be determined by the Marin County coroner's office.
The deaths this week follow those of death row inmates Andrew Urdiales Nov. 3 and Virendra Govin the next day. Those cases were initially investigated as suicides, but the causes of their deaths has not yet been determined.
An email to prison workers obtained by the Chronicle required its nursing staff to attend an "urgent meeting" to discuss "contraband causing serious fatalities/death."
A California Department of Corrections spokeswoman said department officials are "investigating how contraband may have been brought into Death Row at the prison."
Since California reinstated capital punishment in 1978, 79 death row inmates have died from natural causes; 25 have committed suicide; 15 have been executed; and 11 died by "other" means, the San Jose Mercury News reported.
There are 740 prisoners on California's death row.
Corrections Department spokesman Terry Thornton said prisoners can sneak in illegal drugs by various means, but an inside source or visitations would be the most likely scenario.
"Healthcare staff at San Quentin are increasing targeted outreach and education to inmates on the dangers of abusing illicit drugs," Thorton said. "There have been instances of [illegal drugs] getting in through drones, but visitors and staff are unfortunately the main entry point."
San Quentin, one of the most secure prisons in the United States, is located in Marin County north of San Francisco. The prison also houses more death row inmates than any other U.S. facility.