sleuthhound

Etymology

From Middle English [Term?], from Old Norse slóð (“track”) + hound.

noun

1. A working dog who tracks or pursues e.g. a wanted criminal; a bloodhound formerly used in Scotland.
   Sometimes he pursued the wily burn trout with relentless ferocity and the silent intentness of a sleuthhound. Often, however, he would pause and with his finger indicate some favourite stone to Winsome. 1894, S. R. Crockett, The Lilac Sunbonnet
2. (informal) A detective; a sleuth.
   Of course, that may be an accident and couldn't possibly be called a case against anybody; but then we haven't the means to make a real case against anybody. Till the police come we are only a pack of very amateur sleuthhounds. 1922, Gilbert Keith Chesterton, chapter //dummy.host/index.php?title=s%3Aen%3AThe+Man+Who+Knew+Too+Much%2FChapter+6 6, in The Man Who Knew Too Much