LogFAQs > #933547110

I can approach this from the number of people killed. After all, each culprit, except the first, must kill at least one person.

If one culprit already killed 6 people, then the rest of the murders have to be carried out by someone else.
He must be the one who broke into the guesthouse and killed 3 more - George and Maria can't do it.
This leaves Shannon/Kanon and Jessica as the victims, and George and Maria as the culprits.
Geroge can't kill Shannon; so Maria must have done it.
George has to kill someone, so he killed Jessica.

This seems to fit, but I have to check a bit more...