Harry Potter Murder Mysteries

[Calinero]

In the Harry Potter fanfic I'm currently writing, a decent number of characters get stranded inside a hospital surrounded by dementors, cut off from the outside world (long story.) As an added part of the drama, I had planned that one of the charries is a criminal. Shortly before the crisis begins he kills a nurse in the hospital, and the idea was that he would have to hide her body and worry constantly throughout the story about being discovered as the murderer, and grow more and more paranoid culminating in a climax where he snaps and tries to kill people. Unfortunately, it just occurred to me that, as a wizard, he would probably have other means available of disposing of the body. How can I remedy this, and keep the dramatic potential?

Ideas I have considered:

1. The criminal is largely uneducated and not an extremely talented wizard. He might not be good enough at transfiguration to transform the body. However, he is accomplished enough to kill her, and should probably know some spell at least destructive enough to destroy the body. Hmm.

2. The presence of so many dementors dampens their magic, rendering the wizards incapable of casting more powerful spells (or any spells at all.) The con to this is that no such effect has really been witnessed before--however, this could be explained by the fact that this is the largest gathering of dementors ever witnessed. Literally ever dementor on the planet is either at or on its way towards this location.

Other ideas?

[serbii]

3. His (their) wands have been damaged, broken or lost in some way.

4. The nurse is part giant/changeling/fairy/kitsune/vampire/selkie/nymph/veela/werewolf/non-human in general and her body can't be disposed of by human vanishing or transfiguration.

[Calinero]

Ooooh. not so big on 4, but 3 is a definite possibility, especially considering that the two just fought. I'm thinking either 3 or 2 right now.