I need help with the movie "Valentine".?

OK, in the movie Valentine i kinda get confused because i don't know if Dorothy is the one that killed most of people or Adam killed the people because at the beginning when the person that killed Shelly the person's nose bled and Jeremy Melton's nose always bled and Jeremy Melton turned out to be Adam. But Kate shoots Dorothy when Dorothy is wearing the cupid mask and costume, and then Adam is like holding Kate at the end and his nose bleeds. so can you tell me who the real killer is or it could be both of them. AHH. i don't know.