Joseph Naso, 79, former photographer, on trial in "Double Initial" murders of four women in California

(CBS/AP) SAN RAFAEL, Calif. - Opening statements are Monday in the so-called "Double Initial" murder trial, accusing a 79-year-old man with the decades-old killings of four alleged prostitutes in Northern California who had matching initials.

Prosecutors have painted Joseph Naso as a "sexual deviant" who drugged and photographed his unconscious victims, then strangled them and dumped their naked bodies in rural areas.

Attorneys for the state said all of the victims were prostitutes, and all had matching initials: 18-year-old Roxene Roggasch in 1977; 22-year-old Carmen Colon in 1978; 38-year-old Pamela Parsons in 1993; and 31-year-old Tracy Tafoya in 1994, leading to the "Double Initial" moniker.

Prosecutors allege Naso met the women through his work photographing models, CBS San Francisco reports. According to testimony at a pre-trial hearing, Naso photographed nude and partially nude women in lingerie in poses that made them appear dead or unconscious, the station reports.

Authorities around the country were also looking at Naso as a suspect in more cold cases, but none have thus far come to light.

Naso, who is representing himself with the help of a legal adviser, has pleaded not guilty.

Marin County prosecutors have built a significant case against Naso.

Investigators discovered DNA matching Naso's profile on at least one victim, Roggasch. When her body was discovered, Roggasch was wearing panty hose inside out and had a second pair of panty hose around her neck, a third pair in her mouth and a fourth pair wrapped around her mouth, Contra Costa County sheriff's Dep. Tuan Nguyen reportedly testified at a pre-trial hearing.

Nguyen testified that Naso's wife Judith's DNA was found on one pair of panty hose, and semen from two males was found on another. One of the samples likely came from Naso, Nguyen testified, CBS San Francisco reports.

Also discovered were photographs - including images of at least one of the victims in the case - and what prosecutors called a "rape journal" during a search of Naso's Reno, Nevada, house.

Naso characterized the sadistic photographs as his art and said all of his "models" were willing participants.

Near the pile of photos in Naso's home - with mannequin parts and women's lingerie strewn about - investigators said they also found a "List of 10" he had scrawled with descriptions of 10 women, including four references prosecutors believe describe the slaying victims in this case.

There is no indication that any of the six other women referred to on the list have been identified, but prosecutors have said the investigation is ongoing.

Investigators testified previously that Naso kept $152,400 in cash, along with news clippings covering the slayings of Parsons and Tafoya, and other personal items from women, in a safe deposit box.

Complete coverage of the "Double Initial" murders on Crimesider