Just because Breeze is nice, doesn't mean she can't be it. There have been many books were the "nice" people are the villains.
- !*MAJOR SPOILERS FOR THE FIRST BRAVELANDS BOOK*!*
(Such as with Stinger, the Mr. Nice Guy who you thought was awesome and then ended up killing the leader and succesor of the troop.)
From what I'm suspecting with the murderer, I feel like they were mainly trying to frame Storm or something, so they could've of just been doing these things and making the evidence seem like it was Storm who did it, (such as tearing out Bruno's jaw, Breeze saying a large dog dragged her through the woods, etc.) So when Storm would finally get kicked out, they would stop, making the whole pack think Storm WAS the one who did it.