A new book says the BTK serial killer planned to kill an 11th victim by hanging her upside down in her Wichita, Kansas, home. It’s a story police heard from Dennis Rader himself in 2005, but decided at the time to suppress to protect the woman.

The story was made public in “Confessions of a Serial Killer: The Untold Story of Dennis Rader, the BTK Killer,” which has a scheduled release date of Sept. 6. The book was written by professor of forensic psychology Katherine Ramsland.

The author says lust and a desire for fame and power drove Rader to kill 10 people in Wichita from 1974 to 1991.

Rader’s daughter, Kerri Rawson, told the Wichita Eagle her father cooperated on the book because he’s proud of his murders.