Should I feel bad about this?
Ok, So five days ago me and my roomie bought three fish. One for each of us and another to keep them company. Well they *seemed* to get along ok, but by the third day the company fish had a broken barb and by the fourth he was dead and later that day mine also died. I had gone home on the third day and came back on the fifth, so I didn't get to see how they died, or how they looked. I just assumed they had just died randomly, I found out that I was mistaken.

Well two out of 3 fish died and only my roomies was left, so we bought two new fish, another of the same kind as her alive one and a pretty Koi for me. We noticed that her was chasing the two news, but thought he was just playing. Well that was 8 hours ago.

Thirty minutes ago I decided to check on them and I found my poor Koi hiding in the uppermost corner of the tank missing just about all of his precious fins and 3/4th of his beautiful scales. The other new fish was hiding in the lower most corner, also missing scales.

Well...I got got mad so I took my poor baby out and the other fish and put them in a bowl [Only for a little while, I put them back in the tank. I would have left them in bowls if I had a large enough container for them] and then I caught my roomies fish that was torturing the other two. I tried to kill it but it just wouldn't die, so i put it back in the tank, hoping it would leave them alone until I could find an alternate housing for either of them. It was a resilient fish. I Well I checked about 10 min ago and he is dead [the fish], mostly likely because of me. I feel bad that my roomies fish is dead, but happy because now he cant hurt the other fish.

I guess my question is: Should I feel bad about killing my roommates fish, even though it killed two and was torturing two more to death?