It's not Sam's fault- or yours.
After the crash from when Sam's boyfriend, Peter, followed your bus back to Shadyside and threw glass bottles at it, she ended up in the hospital. No one would let you see her- not even her own mother.
But Peter's threat remained stuck in your head 'We're gonna kill you Shadyshit trash'. Peter wouldn't be able to do that, he's skinny, he's lanky, sure he's a football player but he can't really do much. So you didn't take it to heart, until your friends, Simon and Kate, called and said that some sicko with a skeleton mask on had broken in while they were babysitting and started to root through their laundry.
It was like this killer was mocking Heather's death (because she was killed by Ryan Torres who was the original Skull Mask killer.) And immediately, everyone thought it was Peter. So you guys, including Deena and her little brother Josh, drove up to the hospital and demanded to see Sam. It took some convincing but you managed to do it.
After five minutes of being in there, you and Sam got into an argument when you told her to tell her psycho boyfriend to knock it off. Suddenly, Peter came into the room and just watched you two argue, until a knife pierced his stomach..