Hermann-Petersen, 1908. 102p, (Danish).
[Reprinted by Adam Wood, 1999 (English)]
This is one of the earliest feature-length books ever written on the Ripper case, and until recently, one of the most rare. Though the original is in Danish, researcher Adam Wood has published a handsome translated reprint edition (pictured, right) which includes a faithful facsimile of the original. Highly recommended for collectors and serious students of the case.