First off our condolences for the family of the deceased.
I was a VIP visitor of this facility in 2006 and got to sea things that most people don't. While I find the technology used to maintain marine life somewhat fascinating the keeping of cetacea in captive pools is something I strongly disagree with.
This incident just shows what can go wrong and often the case when it does the results are tragic.
Please don't try to compare this to keeping pets. These are not domesticated animals. Even though orcas have been reared in captivity their needs simply cannot be fulfilled by keeping them in concrete pools - no matter the size!
The water quality is far from ideal - a fish released in this pool would have instant gill damage from the chlorine levels! The pools also present a very uncomfortable acoustic environment for these creatures.
If you ask an attendant why some of the (bulls') tails are curved over they will not tell you the truth! The truth is they spend most of their lives swimming in circles near the surface. Without water surrounding the dorsal appendage to provide buoyant support it lays over. A healthy bull in the wild can have a dorsal fin that stands well over six feet tall! Females usually don't have this issue in captivity because theirs is smaller but the larger ones do bend at the tip.
These animals also swim about 150+ miles per day. That's a lot of laps around the pool! They don't like to be be fed but rather hunt and play with their food.
As to why this happens - grabbing a trusted person - is anyone's guess. Frequently other whales can be observed showing a lack of interest in obeying simple commands before something awry occurs. It could be a warning sign, or not. Problem is this is entertainment, and the show must go on.