Since the killer had used liquid nitrogen and a sledgehammer.

I'm suddenly having flashbacks to Jason X...

but he will know about magic slash

Oh, my kind of story!

Um.
Britpick FAIL.

Hey, you should see their Fourth of July parties! Wild!

Severus Snape found a old dairy in the library one night while studying,

[sniff, sniff]
"Merciful Merlin, what IS that smell?"

he finds that the previous owner is hurting the student of the school.

That must be a small school, to only have one student...

anew extention is added to Harry Potter

"Hey, it worked for Otto Octavius!"