According to reports, this whale is responsible for two other deaths. Therefore, he was in a tank where trainers were not supposed to be swimming. I agree with Adam, that we should all wait until Sea World comes out with a statement regardign Tilly's fate, but honestly, what was the trainer doing so close to the pool where Tilly was. If no one was supposed to be swimming with that whale, there was obviously some line she crossed to piss it off. I'm in no way condoning the fact that the whale attacked and killed the trainer, I just don't think everyone should jump to conclusions about "killing it". They should just put it in another part of the "Shamu" exhibit where humn in-water interaction is not a part of it.
Also, the trainers know the risks of working with a dangerous animal. I'm sure they're required to sign releases that detail the possible attack and/or kill situation. It is not the whale's fault that he acted out of instinct. Whales are just like any other intelligent being. If they're sick of doing their tricks or behaviors or some other issue is distressing them, they are going to act out. They can't use words, only actions. The animal's instinctual reaction does not give an excuse to kill it.