A Question...

Why, when someone has committed a murder with an axe, are they then known as an axe-murderer? This does not seem to apply to any other sort of murderers - nobody, as far as I can tell, is known as a knife, gun, book, etc-murderer.
A quick search on google revealed nothing helpful, except for info about Mike Myers, so for now it's going to have to go unanswered. At least until I somehow manage to wrangle up some knowledgeable readers.