Capital Punishment For A Murderous Fish?

I have a murder in my tank. Bubbles was murdered last night. I know who did it. Heimdall. He's now going to be called Loki because he's an evil, evil, murderous fish (and he killed Balder already - check out Norse mythology for that connection). Loki also happens to be the smallest fish in the tank. He's managed to kill two fish. Bubbles was the third largest fish in the tank easily 4 times the size of Loki, yet Loki, the little bastard, managed to kill bubbles. Now I have to consider my next course of action. Do I take Loki out of the tank before I'm down to just him? Do I just leave him and hope his appetite for murder has been quenched (which it probably hasn't - serial killers rarely ever stop on their own)? Or do I make him stand trial for his actions and let a jury of his peers sentence him to pay for his crimes? Is Capital Punishment far to cruel for a serial killer goldfish? We have proof of two fish murders that have happened in my tank, I have no idea how many other tank mates he may have killed in his previous tank. Does this fish deserve the death penalty (a flushing)?