I agree that Ruby likely isn’t the killer, although she probably will be able to phase into her wolf form. Neither do I think the murderer is Regina or Rumpel. If they’re smart, they’ll keep a low profile to avoid incurring any further than is already owed them. What if the killer is King George? The actor who plays him is supposed to be in this episode, and we know he’s not adverse to killing others. We already saw King George try to kill Prince Charming, and we’re about to see him try and kill Snow White and Charming’s mother in 2×3. Also, since King George is the district attorney of SB, he could try to point the evidence to Ruby, who is a known werewolf.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy