A probation officer testified Wednesday that he found a diary documenting rapes and sexual assaults of underage girls while he searched the home of a man suspected of being a serial killer.

Nevada Department of Public Safety probation officer David LeBaker made the disclosure during a preliminary hearing for Joseph Naso, who was accused in the "Double Initial" killings.

LeBaker said he found an aluminum clipboard containing the diary on Naso's dining room table in 2010. It detailed assaults of an underage girl on a Greyhound bus in Arkansas, a girl in Kansas and others, he said.

"I briefly went through it and read a few small paragraphs," LeBaker testified. "I then notified my supervisor and said, 'you should see this.'"

Naso, 78, was acting as his own lawyer in the case. The former photographer has pleaded not guilty to four murder charges involving slayings in the 1970s and 1990s.

White-haired and wearing leg shackles, he sat alone at the courtroom defense table.

During cross-examination, Naso questioned LeBaker's knowledge of sexual assault laws in those other states, noting the age of consent and other laws can differ.

Naso asked LeBaker if he was sure what he read constituted sexual assault.

"If I heard that someone digitally penetrated a young woman, I would say that's a sexual assault," LeBaker said.

The preliminary hearing is providing the first in-depth look at the prosecution's case against Naso and his lifestyle.

Nevada probation Officer Wesley Jackson testified that he arrived in April 2010 to check Naso's Nevada home for violations of his probation agreement and found food rotting on the kitchen counter and debris strewn about.

All the bedrooms were locked, and Jackson said Naso resisted opening them for a time.

In Naso's bedroom, Jackson said, he found mannequin parts and a full mannequin clad in a red dress. Women's lingerie was in the dresser drawers.

In a connected bedroom, Jackson and his fellow officers found a "List of 10" that contained scrawled descriptions of 10 women, including four references that prosecutors believe described murder victims — Roxene Roggasch, 18, Carmen Colon, 22, Pamela Parsons, 38, and Tracy Tafoya, 31.

The matching letters of each woman's first and last names gave rise to the "Double Initial" moniker for the case.

Six other women referred to on the list had not been identified as of Wednesday, but prosecutors say the investigation was ongoing.

Near the list were numerous photographs showing nude women posed in unnatural positions who appeared dead or unconscious, authorities said.

Some of the photos had been pasted to poster board, with some showing only the lower halves of the bodies.

Further searches of the home turned up a box of knives and guns hidden behind a refrigerator in Naso's garage, authorities said. Naso was forbidden to have weapons due to probation from a felony larceny conviction in California.

Investigators have said Naso might have used his then-wife's panty hose to strangle Roggasch, a prostitute whose 1977 murder went unsolved for decades.

Colon's decomposed body was found near Port Costa 1978 by a California Highway Patrol officer in Contra Costa County. Authorities have said DNA evidence collected from her fingernails could tie Naso to her slaying.

Parsons' strangled body was found in Yuba City in 1993, where Naso was living at the time with his mentally ill son. Court documents state that Naso had photographed Parsons.

Tafoya was killed in Yuba City when Naso lived there. Her body was found on the side of Highway 70 near Marysville Cemetery in 1994.

Authorities previously said Naso was being investigated for possible links to New York's "Double Initial Murders" of three girls in the early 1970s.

However, that investigation has ended.