An ice axe, used by mountaineers to climb snowy/ice mountains, looks quite threatening, and no doubt can be used to cause grievous bodily harm by persons with little or no training.
An ice pick can easily do the job, though... check out the Wikipedia article on 'Lobotomy'. Walter Freeman experimented with an ice pick, shoved up into the eye socket above the eye, and perfected the procedure using a similar surgical instrument known as a leucotome. He turned lobotomy into a mass production procedure, often doing a half dozen or more a day in his visits to mental hospitals.
If your objective is to kill someone, obviously you do not perform the controlled motions involved in a lobotomy, you just shove the pick in and go for it with gusto and abandon.
Or just go for the heart. Actually requires a tad of skill to do in one quick stroke, but not much.
The ice pick has the advantage of being easier to conceal.
Hate to bring this up so late in the conversation, but there is such a thing as a 'pickaxe'....
Lac lactis in primoris (milk in first).