Satsujin Sha

You were bored so you decided to go to your best friend's house. You stayed there for hours and hours and didn't notice the time going by; eventually it was pitch black outside and he said you should stay a his house as there was suspicion of a serial killer. That was enough to convince you and so you agree. He goes to take a shower and you go through his things, trying to find ways to entertain yourself while he left you alone. As you look at everything he as he find a mask-similar to the serial killer on the news. "I didn't think you were this nosy..."