WICHITA, Kan. (AP) — A man who bought a used copy of the book co-written by BTK serial killer Dennis Rader has discovered inside the book one of the killer's drawings showing a bondage rack and rope.

Rader is known for binding and torturing his victims. The crayon-and-ink drawing has his name and a July date on it.

The Wichita Eagle reports that research scholar Katherine Ramsland says the artwork appears to have been made by Rader. She co-wrote with him "Confession of a Serial Killer: The Untold Story of Dennis Rader, the BTK Killer."

She says Rader sends bookplates to pen pals and people who've bought the book.

The Kansas Department of Corrections says inmates are allowed to send and receive mail as long as it's not a security risk or sexually related.

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Information from: The Wichita (Kan.) Eagle, http://www.kansas.com