Well, okay. I performed the arduous task of clicking on the link I provided earlier, then cutting and pasting the exact information you requested, which was on that very page. Whew.
BODYCOUNT: 8 female:5 / male:3
1) Young girl falls to her death after prank backfires
2) Female found dead- stabbed to death with broken glass (off-screen)
3) Female has throat slit with shard of glass
4) Female stabbed to death with shard of glass
5) Male dies when van goes over a cliff and explodes
6) Female killed with axe
7) Male decapitated with axe
8) Male dies from head wound inflicted with axe
I couldn't find much on the ending, but here's what I can piece together from memory and my searching:
Spoiler:
The killer is Alex Hammond (Michael Tough). At the beginning, his older sister Robin, while playing in an abandoned building, falls to her death in front of him and the other kids (the other kids were teasing her, and more or less caused her accident). Six years later, he flips out and kills them all, but falls to his death before he can finish off his other sister, Kim (Jamie Lee Curtis).So, to answer your question, all but one of the deaths were caused by him...if you don't count the mysterious disappearance of Mr. Hammond (Leslie Nielsen).
In the future, I suggest simply looking up the movie at www.imdb.com or typing "Prom Night Body Count" in Yahoo search. There are tons of fans of the genre, and the info isn't that hard to find.