[cheebacheeba]

Make a plastic mould, in the shape of your preferred weapon, say a hatchet, dagger or mallet
Fill with water, freeze. The "mould" would have to be fairly thick so as to make strong ice weapons. Handle only with plastic gloves...and leave when you're ready to kill someone relatively nearby, you may need to case the situation, and figure a good location, or even consider investing in a freezer unit say, in the trunk of your car.
When ready, remove the weapon from the mould. Torch the mould on your way out. Kill your victim, drive/walk away, let it melt inside their wounds/nearby.
The mallet would probably be best, or you could just bake bricks of ice to throw? I'd go with the mallet.

There you go, a MURDER weapon.