While it may have sounded a bit too difficult, it is not that difficult to crack.
The murderer is Marcus.
The notes were found in the Compound, Art Room, Restroom, Underwater Room, Smoking Lounge and Makeup Room.
Now, if we just look at the first letter of each, we will have - C, A, R, U, S and M.
If you arrange the letters, you will get the name Marcus.