Methinks your "friend" lied to you about that vicious dog that should be PUT DOWN and your "friend" should be made to pay. Period. No excuses. This was a horrible thing to happen to poor, sweet, fragile, little Commodus and for you to have to see it yet is unthinkable! I'm so sorry that this happened but as someone on PT said, it's highly improbable to keep a vicious animal separated from other animals. Check out my thread about Kiara, the cat whose "family" tried to keep her separated from their vicious dog and she was attacked twice and had surgery twice as a result of those attacks.

Your heart was in the right place and you wouldn't have taken the dog in had you known how vicious it was and that the life of your precious Commodus would have been in jeopardy. Be at peace w/yourself about that. And know that Commodus is now at peace and playing hard at the Rainbow Bridge without fear.