Two death row inmates at a California prison were found dead from apparent suicide less than 48 hours apart, California Department of Corrections and Rehabilitation officials said.

Andrew Urdiales, an ex-Marine convicted and sentenced to death for murdering five women in Southern California between 1986 and 1995, was found unresponsive in his cell around 11:15 p.m. PST (2:15 a.m. ET) Friday during a security check, officials said in a press release.

He was pronounced dead shortly after midnight.

Around 10:15 p.m. PST (1 a.m. ET) Sunday, officials found convicted killer Virendra Govin dead in his prison cell. Govin had been on death row for the murder of four people.

Both inmates were housed in single cells at San Quentin State Prison, and the deaths are being investigated as suicides, officials said.

Urdiales was sentenced to death on Oct. 5 for the murders of 23-year-old Robbin Brandley, 31-year-old Maryann Wells, 29-year-old Julie McGhee, 20-year-old Tammie Erwin and 32-year-old Denise Maney.

Authorities said Urdiales killed the women while he was stationed at various military facilities in Southern California.

The 54-year-old was previously convicted for the murders of three Illinois women, 21-year-old Cassie Corum, 25-year-old Lori Uylaki, 22-year-old Lynn Huber.

Urdiales was sentenced to death in Illinois in 2004, but the sentence was commuted in 2011 to life in prison. He was then extradited to California to stand trial for the Southern California murders. He was convicted in May and sentenced to death in October.

Govin, 51, had been on death row in California since January 2005 after he and his brother, Pravin Govin, were convicted of killing four members of a family, including two teens, and then setting their Hollywood Hills home on fire. Pravin Govin has been on death row since September 2005.

Officials said they do not believe Govin and Urdiales' deaths are related.

There are currently 740 inmates on death row in California. Prison officials said since capital punishment was reinstated in 1978, 25 death row offenders have committed suicide.