"I just want you to know there are worlds out there, safe in the sky, because of her. That there are people living in the light, and singing songs of Donna Noble, a thousand million light years away. They will never forget her… while she can never remember. And for one moment… one shining moment… she was the most important woman in the whole wide universe.”
if you want to kill someone stab them with an icicle because the icicle will melt and then there will be no murder weapon
Better yet, make like one of my favorite short stories and murder them with big frozen leg of lamb and then cook the lamb.
Then when the police arrive offer them something to eat and then have the police eat your murder weapon.