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Marin Independent Journal, Alan Dep, File, Associated Press
FILE - In this April 13, 2011 file photo, Joseph Naso appears in Marin County Superior Court during his arraignment on murder charges in San Rafael, Calif. Prosecutors were expected to begin presenting their case Tuesday, Jan. 10, 2012 against Joseph Naso, a 78-year-old photographer charged with killing four Northern California women with matching initials in the 1970s and 1990s.

SAN RAFAEL, Calif. — A probation officer searching the home of a serial killing suspect in 2010 says he found a diary documenting rapes and sexual assaults on underage women.

Officer David LeBaker testified Wednesday during a preliminary hearing in the murder trial. He says he found an aluminum clipboard on Joseph Naso's dining room table.

The 78-year-old Naso is defending himself against four murder charges for slayings in the 1970s and 1990s. He has pleaded not guilty.

LeBaker says he read the diary, noting paragraphs that detailed assaults on an underage girl on a Greyhound bus in Arkansas, another on an underage girl in Kansas and other cases.

During his cross examination, Naso questioned LeBaker's knowledge of sexual assault laws in these other states, noting that different states have different age of consent and other laws.