Brook Carey was the warden of California Institution for Women (CIW) Frontera for a year from March 1975 until February 1976. She applied for the job almost on a lark having had no training or experience working in the law enforcement field in any capacity. To her surprise she landed the job only to find out later that she was hired to fail. The book The Accidental Warden (2008) is about her year of being the warden at the only women's prison in California at that time. It was during this year that four Manson Family women were incarcerated at the prison, Atkins, Brunner, Krenwinkel and Van Houten.
The book was okay, a short and easy read. Prison politics make up the majority of the book as well as the things that Carey felt she had done to improve the system and make it work better. There are bits about the Manson Family women and even a chapter on a visit she made to Manson while he was in San Quentin. She went to visit him to tell him the women did not want him to try to make contact with them any longer. They felt that further contact would hurt their chances of getting parole, they just wanted to do their time and get out. (We know that hasn't gone so well!)
The one thing in the book that I had never heard about was a threatening letter sent to the FBI, presumably by a Family member on the outside, saying that unless all the Family members were released by a certain date, five people a day would be killed. They already had the first five chosen. Here is an image of a transcription of the letter as it appears on pages 90 and 91 of the book. The letter was postmarked Chicago Illinois.
I tried to find if this threat ever hit the newspapers and I could not find anything about it. As this happened around June and July of 1975 before Squeaky tried to assassinate President Ford and before Sandy Good and Susan Murphy were arrested for writing all those letters threatening corporations and the heads of those corporations. I'm inclined to think that it was Sandy and Squeaky who were behind the letter being sent even if they did not send it themselves.
While doing the newspaper search I found an article that tells about Manson threatening to send five people to kill Nixon and Reagan. There seems to be a theme with the number five here between the two threats. This article is from the Edwardsville (ILL) Intelligencer, September 11, 1975. Had Squeaky never tried to assassinate President Ford we probably never would have known about this threat either.