Los Angeles police have obtained decades-old taped conversations between a Charles Manson family disciple and his lawyer.
Detective David Holmes said the department had the tapes for a couple of weeks and the robbery-homicide division and the Los Angeles County district attorney's office were analysing them.
A judge in Texas ruled in March that Charles "Tex" Watson waived his right to lawyer-client privilege when he allowed his lawyer to sell the eight cassette tapes to an author nearly 40 years ago for a book on his life.
The tapes, which were converted to electronic audio files, are being reviewed to determine whether there is evidence that could resolve unsolved murders.
Watson, who sought to prevent turnover of the tapes, is serving a life sentence for his role in the 1969 murders of actress Sharon Tate and six others.
He has said the Manson family was not responsible for any other killings.
The tapes were discovered last year by a trustee handling the Chapter 7 bankruptcy case of the law firm were Watson's lawyer Bill Boyd was a partner. Mr Boyd died in 2009.