Notes (Misthalin Mystery - 3)

The Notes are an item that was found outside the kitchen doors during the 2016 Hallowe'en event. It contains a riddle.

Transcript
Hear at first these words. Each murder you witness helplessly from start to end. As you fail to solve the final letters of this quiz. Razor sharp like a gemstone is the blade of my knife. The last sound you hear will be your scream's echo. Heed that I will have the final word in this thriller.