mmmm
Solve this riddle and you could be a psychopath!

Timeline as I see it:
The mother dies of some random reason (not murder)
The funeral happens
the girl meets a guy she likes and they date
the girl doesn't get the guy's number so they have no way of communicating
the sister gets murdered.
Guy would be a noobs answer

actually my new answer is the mother
the mother fake her death and she will get revenge people were mean to her
XD, but thats not the case scar.