How do you get the good ending?

How do you get the good ending?

I've tried different ways but always die or get the bad ending. I killed the killer to get the key and then had to kill Melanie for the key... Bad ending. I sprayed the killer with the spray can and tied him up, just like all the hints tell me to. I talked to him too, just like the hints say to. The hints say that the killer will save me from the gas? But he doesn't? The killer tells me when I talk to him that he told Melanie I was the butcher and that she believed him... That's why she tried to kill me with gas. I tried to reason with Melanie (who was wearing the pig mask and in the bathroom) but she won't listen or open the door... How do I get Melanie to come out and how do I get the good ending??