If Nina didn't do it, William didn't do it, Johnny didn't do it, and Karen didn't do it; that only leaves Melody.
Oh. I didn't notice that I'm already cornered by my reds. anyways I'll give you these reds
There was something in the kitchen that is noticed by William at the 5th murder
There are 5 alive members after the 1st Murder
There are 4 people inside the building (end of 2nd murder)
There are 3 people inside the building (end of 3rd murder)
Now it makes almost perfect sense. Karen is the killer.
#1: She hurt herself enough to slowly bleed to death, but stay alive long enough to kill everyone else.
#2: She pushed Johnny out the window, and hid in the bathroom.
#3: After she hurriedly got out the glass pieces from her clothing and hair, she saw Melody, killed her and hid again.
#4: She pushed Nina and Will down the stairs, cracking open Nina's skull, causing slow death.
#5: She and Will got into a fight in the kitchen. Karen killed Will, and then died from her previous blood-letting wound.
Now it makes almost perfect sense. Karen is the killer.
#1: She hurt herself enough to slowly bleed to death, but stay alive long enough to kill everyone else.
#2: She pushed Johnny out the window, and hid in the bathroom.
#3: After she hurriedly got out the glass pieces from her clothing and hair, she saw Melody, killed her and hid again.
#4: She pushed Nina and Will down the stairs, cracking open Nina's skull, causing slow death.
#5: She and Will got into a fight in the kitchen. Karen killed Will, and then died from her previous blood-letting wound.
Karen didn't died from a cut/stab
There are two things that William saw at the 5th Murder, a 250 ml empty bottle of blood, and a light switch at the floor.
#1: She used the 250 mL bottle of blood to fake her death.
#2: She pushed Johnny out the window, after she hit the secret switch on the floor, and hid in the bathroom.
#3: After she hurriedly got out the glass pieces from her clothing and hair, she saw Melody, killed her and hid again.
#4: She pushed Nina and Will down the stairs, cracking open Nina's skull, causing slow death.
#5: She and Will got into a fight in the kitchen. Each got seriously wounded, and died from their respective wounds.
#1: She used the 250 mL bottle of blood to fake her death.
#2: She pushed Johnny out the window, after she hit the secret switch on the floor, and hid in the bathroom.
#3: After she hurriedly got out the glass pieces from her clothing and hair, she saw Melody, killed her and hid again.
#4: She pushed Nina and Will down the stairs, cracking open Nina's skull, causing slow death.
#5: She and Will got into a fight in the kitchen. Each got seriously wounded, and died from their respective wounds.
by I meant by switch, it looks like this and it isn't connected into a wire.
Spoiler:
There's no secret switch, it's just a switch lying at the floor. (5th murder)
Karen didn't died from a wound
There is only one culprit The bathroom and Karen's room are close to each other
Murder #1 Johnny was the one who turned off the game, also the last one to go up
Nina checked Karen's room
Melody checked the bathroom
After the end of the 2nd Murder, No one is dead yet
The murder didn't occur after William returned from taking a pee outside
Murder #2 Melody is the nearest one to Johnny
At the end of the 2nd murder, there are 4 people in the building
Johnny died from the fall
Murder #3 Karen's room is the nearest one to the Bathroom
At the end of the 3rd murder, There are 3 people inside the building
Murder #4 At the end of the 4th murder, There are 3 dead people in the story.
Murder #5 William didn't commit suicide
William saw a light switch lying on the floor
There are no survivors
After the 5th Murder, there are no survivors - they have all died, the culprit commited suicide.
Other info Karen didn't commit suicide
Karen's death wasn't the effect of cuts or wounds. Not a single blood came out
Nina knew who is the culprit after checking Karen's room