Talk:Scott McCall/@comment-82.222.218.25-20120802081115/@comment-195.216.6.241-20120802145725

Yes but that was before Derek found out that Peter killed Laura; then he accepted it as Peter claimed it was an accident but in the final episode, when Scott came to rescue Derek from being tortured by Kate and her buddies, Scott reveals that Peter obviously killed Laura deliberately, thus when they ran in to Peter a short time after (only minutes really), Derek was still angry and feeling betrayed, hence why he killed Peter.

Derek did hesitate before killing Peter but then Peter taunted him and Derek let the anger take over. He was facing the man who had killed his sister, the only remaining member of his family - it's understandable that he wanted to kill him himself.