Disclaimer: I own nothing but the twisted life of Peter Campbell.
I left the ending a mystery so people could create their own version, but I'm getting so many PMs asking about it that I decided to give you my version of how things happened.
Some of you noted how young Edward was and how it wasn't possible for him to have so many victims, kudos to you for picking that up. Also, I got a lot of questions about how come Peter never recognized Edward in the parking lot, if he was behind everything after all. Did it ever occurred to you that Edward was wearing a disguise? He spoke to Peter in Spanish too. And then there was the fact that Edward tortured Peter instead of just killing him. Edward had killed Caius, Marcus and Aro at cold blood, why not Peter? He was his biggest obstacle to get to Jasper after all...
Well, this is how I see it:
Peter was lost in the darkness, but he could stand being visible. He trained Edward when he found him during a book tour, noticing how he kept hiding in the shadows. When Peter visited Alice (the day of the photo Jasper found in the last chapter), he found out what Edward was doing under Bella's oppression.
Peter was actually the one behind Alice's death. Did you notice how Edward never said he was the one that came up with the plan to make Alice kill herself? Bella assumed it was Edward, but he cared about Alice and couldn't kill her. Peter told Edward to make it look like she had done it herself. Edward was pressured by not only his mother, but Peter as well, which force him to give Alice a hand, or a kick to the chair in his case. Alice had been his first victim, the other girls were actually Peter's tests while he trained Edward.
In essence, Peter was the mastermind that lost control over his creation, as simple as that. He loved Jasper, but once it was out that Peter knew Bella and Edward, there was no going back for him. His secret was out, and no one could find out.
I could write a whole other fic about Peter's background, but I won't. I like how things ended.
Thanks for reading and I hope this clears things up a bit.