Accused California serial killer makes own closing argument at trial SAN RAFAEL, California (Reuters) - An accused California serial killer delivered the closing argument at his own capital murder trial on Friday, insisting as he has from the start of the proceeding that the prosecution's case is built on nothing more than "opinions and theories." Joseph Naso, 79, charged with first-degree murder in the slayings of four prostitutes dating back to the 1970s, has acted as his own attorney during the nearly two-month trial in a Marin County, north of San Francisco, but declined to take the witness stand in his own defense. The balding, retired photographer has admitted a penchant for taking pictures of women in nylons and high heels, some of which he has exhibited in court, but maintains he never killed anyone. After weeks in which prosecutors presented the testimony of roughly 70 witnesses, Naso called only handful of individuals to the stand, including a woman who once posed for him as a model and an artist that the defendant asked to vouch for his work. Prosecutors presented their closing arguments on Wednesday, summarizing their evidence for how they said Naso isolated his victims, sexually assaulted and strangled them, disposed of their bodies in remote areas and then documented his crimes in a journal. After a one-day recess in the proceedings, it was Naso's turn to summarize his case for the jury, which he did as he stood under guard behind a podium, dressed in a gray sports jacket, a white shirt and a red-and-gray striped tie. "The prosecution has focused their entire evidence not on weak circumstantial evidence, but on weak opinions and theories," he said. The prosecution has constructed this entire case against me. It all equals one thing - guesswork. Naso said prosecutors had no proof he murdered any the four northern California women. But he did concede that DNA found in the pantyhose worn by one of the women, Roxene Roggasch, when she was found dead might justify the conclusion he had sex with her. Roggasch, 18, and Carmen Colon, 22, were slain in the 1970s. Two other victims, Pamela Parsons, 38, and Tracy Tafoya, 31, were killed in the 1990s. Why is my DNA on the pantyhose? Naso asked, reading from a yellow sheet of notes. Even if it was on there, all it proves is I may have had sex with her, but I didn't kill her. The prosecution can't prove that. Naso could face the death penalty if he is convicted of any more than one of the "alphabet murders," so named because the first and last name of each victim begins with the same letter. Investigators began to tie Naso to the murders in 2010 after law enforcement officers visiting his Nevada home while he was on probation for an unrelated felony theft conviction found ammunition there. A further search of his Reno house turned up what prosecutors have described as diaries of sexual assaults, a list of 10 victim dumping grounds and hundreds of photographs of scantily clad women, many appearing dead or unconscious. Judge Andrew Sweet regularly admonished Naso throughout his closing argument, as he has throughout the trial, for violating court rules. Reporting and writing by Ronnie Cohen; Editing by Steve Gorman and Andre Grenon