That's the danger of relying on the internet for your information, if you're truly interested in being a scholar; it can indeed be a helpful tool, but nearly all
sources taken from the 'net should be checked against more authoritative sources, if at all possible. All printed sources I've seen claim it as having been written by von Grosse (with one possible exception which I only very vaguely recall) and translated by Will. Montague Summers has it as such in his bibliography of the Gothic tale; and Joshi (ASHiL
, p. 85, n.1) notes "Among von Grosse's other works are Der Dolch
(translated as The Dagger
Incidentally, here's another source for things Gothic: http://members.aol.com/gothlit/gothicbib.html
Part of the problem with Horrid Mysteries
is that the translation is simply horrendous: repetitive, with awkward sentence structure and poor word-choice, which often leads to completely nonsensical sentences, etc. As I recall, Varma had some comments on this aspect of it, concerning Will... but I could be misremembering here, as it's been at least 10 years since I read his comments on this novel.