Writing A Completion Ofcommunity Service Letter I'm Writing A Short Story And Need A Good Motive For The Murderer In It.?

I'm writing a short story and need a good motive for the murderer in it.? - writing a completion ofcommunity service letter

I write a little story about four friends who congratulate you on a beach house in the summer to her college diploma. Then, one after the other, with one exception, all die, but when the last survivor, he discovers the identity of the murderer. Please someone a good end of the story, like all my ideas are very predictable. Please enter a valid reason for the murderer, they kill them all.