SAN QUENTIN, CALIFORNIA: Known as one half of “The Sunset Strip Killers,” Douglas Daniel Clark, who was sentenced to death for the six grisly murders he committed in 1980, has died in prison from "natural causes."

Clark, who was housed at San Quentin State Prison, had been hospitalized when he died Wednesday, October 11. While California prison officials said his death was due to natural causes, the Marin County coroner’s office is still investigating the official cause of death.

The 75-year-old Clark was convicted of six counts of first-degree murder, one count of attempted murder and one count of mutilation/sexual contact with human remains. He was admitted to death row on March 24, 1983, but California ceased death row executions in 2006.

Clark and his accomplice, Carol Bundy, earned the moniker “The Sunset Strip Killers” after terrorizing the Los Angeles area dismembering and decapitating multiple young, vulnerable women in the summer of 1980.

Their murder spree lasted for just three months from June until August of that year.

Bundy, who died at Central California Women’s Facility in 2003, was sentenced to life without parole while Clark was sentenced to death in 1983.

When did Douglas Clark begin his murder spree?

Clark and Bundy targeted girls as young as 15 and preyed on weak and downtrodden women during their murder spree, according to Daily Mail.

Clark routinely brought back sex workers to the couple's apartment for threesomes as part of their "intense sadomasochistic relationship.”

At one point, Clark developed desires for an 11-year-old neighbor, and Bundy helped in luring the youngster into their home to pose for pornographic pictures.

From then, his desires 'escalated' to the point where he told his partner that he wanted to kill a girl while they were having sex, and Bundy even got two firearms for him to use.

One report claims that Clark wished to experience a desire of murdering a woman while having sex and experiencing her "vaginal contractions during the death spasms."

How many women did Douglas Clark and Carol Bundy kill?

Clark and Bundy are believed to have killed at least seven people during their months-long killing spree, and there may have been more who were not found or identified.

According to reports, they both confessed to police about further homicides. During the investigation, it was also revealed that after murdering the women, Clark would use their corpses for sexual gratification.

In the end, Bundy was the one to confess her crimes to co-workers and the police, incriminating her partner in the process and leading to their imprisonment.