User blog comment:MrAnonymous/Why is Scott being such an ass with Derek?/@comment-69.249.106.193-20120612161913/@comment-49.248.7.26-20120619090700

There was a good chance that Scott killing Peter wouldn't have cured Scott (it was mere hearsay, perhaps a werewolf urban legend). Derek couldn't take that chance, coz if the legend proved to be untrue, Scott would be the alpha, which he would find hard to control.

One question they never answered is: Who did Laura Hale kill to become an alpha werewolf?