By Dennis L. Breo and William J. Martin. With a postscript by Bill J. Kunkle, the chief prosecutor in the Gacy case; Martin was the prosecutor "who put Speck in prison for life," and Breo "won an award for his coverage of the crime." (You can hear Breo talk more about that, and the book, on WGN right here.) The book came out around the 50th anniversary of Speck's notorious rampage and at over 500 pages, it's probably the deepest dive into those horrible events.
This paperback has a few scuffs and dings to the edges of the covers, foxing to the page edges, and a cracked spine, but the pages are tight; it's a fine reading copy.